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Gallery, Projects and General => The Design Shop => Topic started by: BillTodd on April 03, 2012, 03:25:18 PM

Title: 3d indicator design
Post by: BillTodd on April 03, 2012, 03:25:18 PM
Sneak preview of my 3D indicator design.

Title: Re: 3d indicator design
Post by: BillTodd on April 03, 2012, 05:21:24 PM
Finalising the design of the body.

Two parts Body of aluminium and Shaft of steel will be easier to make.
Title: Re: 3d indicator design
Post by: Deko on April 03, 2012, 05:24:15 PM
Looks good Bill. How do'es it work? Ball on each end of the probe ? :scratch:  Giza clue Bill, giza clue. :poke:

Cheers  Dek
Title: Re: 3d indicator design
Post by: BillTodd on April 03, 2012, 05:29:33 PM
I'm still finesse-ing the design of the probe ATM (I want it to be easily replaceable without taking the whole thing apart )

I'll reveal all when I'm done ;)

Bill
Title: Re: 3d indicator design
Post by: BillTodd on April 04, 2012, 05:37:00 PM
Still not quite worked out the probe bit yet, but you should be able to work out how it is supposed to work, from this section:

Title: Re: 3d indicator design
Post by: andyf on April 04, 2012, 06:53:57 PM
Hi Bill,

What advantages do you see for this 3D design over your earlier co-ax indicator?

No criticism implied - just curious, that's all.

Andy
Title: Re: 3d indicator design
Post by: BillTodd on April 04, 2012, 07:01:52 PM
Quote
What advantages do you see for this 3D design over your earlier co-ax indicator?
It does a different job. 

This is an edge finder, allowing any face in X, Y or Z planes to be located easily.

It was inspired by this Haimer device:

Title: Re: 3d indicator design
Post by: andyf on April 04, 2012, 07:06:21 PM
Thanks, Bill. Now I understand.

Andy
Title: Re: 3d indicator design
Post by: Joules on April 05, 2012, 09:53:02 AM
Nice drawing and concept, but not sure I can figure out how the probe gimbal works.  What keeps it in the centre under a side load.  I could understand a ball joint ?
Title: Re: 3d indicator design
Post by: Joules on April 05, 2012, 09:59:39 AM
Ahhh, the penny dropped, two caged bearing races slide over the sandwiched plate....
Title: Re: 3d indicator design
Post by: BillTodd on April 05, 2012, 11:51:30 AM
Ahhh, the penny dropped, two caged bearing races slide over the sandwiched plate....

 :thumbup:

Title: Re: 3d indicator design
Post by: Brass_Machine on April 05, 2012, 01:59:06 PM
I watched the video. What a neat bit of kit. I would be interested in building one and helping you test!

Eric
Title: Re: 3d indicator design
Post by: BillTodd on April 05, 2012, 04:48:03 PM
Making the probe replaceable has me puzzled ATM.

The Haimer one which has a gimballed probe which cannot rotate , so they screw their probes in position. I rejected the gimbals idea because is would be difficult to make. My linear slide is a simple thrust washer sandwiched between two thrust bearings  so has 3 degrees of freedom (X, Y and rotation). In addition the probe has another degree of freedom (Z) and is also free to rotate.

I'm thinking about  clamping the probe in a collet like arrangement requiring two spanners to fit (fiddly, but this is DIY  ;))

Quote
I would be interested in building one and helping you test!
It's still in the idea/development stage ATM so I would not encourage you to commit to metal just yet. (machining pixels is faster and cheaper )

I'll post drawings when I'm done
Title: Re: 3d indicator design
Post by: BillTodd on April 11, 2012, 05:38:47 PM
The latest incantation has bulked up a bit to accommodate a removable probe (held in place by a small magnet)

Still not quite there but getting close.
Title: Re: 3d indicator design
Post by: Divided he ad on April 12, 2012, 05:27:11 AM
Excellent concept, very neat design Bill :clap:

Gotta love the magnet idea  :smart:



I purchased a two very small DTI (1" clock face) second hand from a booty a while back with a view to making your coaxial indicator.... Well, I was going to have a go! (Still on the tuit list)

Now I may have a use for the second one  :ddb:



Watching with great interest.... And I'll be nudging you for names of suppliers for the thrust bearings etc too  :poke:   :)






Ralph.
Title: Re: 3d indicator design
Post by: BillTodd on April 12, 2012, 08:36:10 AM
Quote
Gotta love the magnet idea

Really? I've gone off the idea after a thinking about it.  If/when a bit of swarf finds its way up the tube it'll cause chaos and be difficult to remove

Bill
Title: Re: 3d indicator design
Post by: andyf on April 12, 2012, 08:51:03 AM
Having a screw-in pointer (or a grubscrew fixing) might give a firmer fixing, Bill. One held by a magnet would have to be a very good fit in its hole to stop it waggling a bit from side to side.

Andy
Title: Re: 3d indicator design
Post by: BillTodd on April 12, 2012, 10:25:46 AM
Having a screw-in pointer (or a grubscrew fixing) might give a firmer fixing, Bill. One held by a magnet would have to be a very good fit in its hole to stop it waggling a bit from side to side.

Andy
Yes you're quite right.  A screw in one would be my preferred way, but I can see no way to stop the lower taper (the bit with the magnet above) turning.  A clamp with a grub screw might be the answer .

Bill
Title: Re: 3d indicator design
Post by: Divided he ad on April 12, 2012, 02:31:41 PM
Well I liked the magnet... But I see the points about the swarf and flex.

A good fit would definitely be required!


How about the use of a tommy bar through or into the receiver so you can screw one in still?


Just a thought...




Still wanna make one  :)






Ralph.



Title: Re: 3d indicator design
Post by: BillTodd on April 12, 2012, 04:04:36 PM
Here's an animation , just in case anyone was still wondering how this works:
(http://wktodd.webspace.virginmedia.com/animations/wpimages/wp0593df82.gif)
Title: Re: 3d indicator design
Post by: philf on April 12, 2012, 04:31:29 PM
Very Nice Bill  :clap:

What have you modelled it in?

Phil.
Title: Re: 3d indicator design
Post by: Miner on April 12, 2012, 05:22:15 PM
Bill,
Since you know about the Haimer 3D "Tastors", Then you probably already know this. However many here won't. The real Haimer's have an adjustment feature so the the tool gets properly zeroed to the centerline of the spindles rotation. They also require a dedicated tool holder like a endmill holder. Any R-8 that still has the alignment set screw inside the taper is no problem, Since the tool holder will only fit the taper in one position. Without that, You would need to permanently mark the tool holder and spindle so the tool is at the same position each time it's used.

After buying mine, I contacted Haimer to see if I could get a exploded view of the internals to find out how the internal construction works. I never did get anything back from them. The removable cover on mine is factory sealed. so I'm not about to open it up.

Glacern Machine Tools also show a digital model and how their used.

Pete
Title: Re: 3d indicator design
Post by: rowbare on April 13, 2012, 01:36:50 PM
US patent 5365673 has a drawing of the Haimer Taster.

bob
Title: Re: 3d indicator design
Post by: Miner on April 13, 2012, 02:25:17 PM
Rowbare,
 :beer: Awesome man, Another of lifes questions finally answered. No wonder these units are so heavy for their size. There's a lot packed inside them. Thanks again.

Pete
Title: Re: 3d indicator design
Post by: Topos on April 20, 2012, 09:45:43 AM
Add my standing Ovation to a super presentation of a wonderful design. :clap:
Title: Re: 3d indicator design
Post by: BillTodd on April 20, 2012, 03:53:34 PM
Add my standing Ovation to a super presentation of a wonderful design. :clap:

Thanks  :)  :beer:

The thrust washers and bearing balls have arrived, and I finished re-painting the kitchen so, hopefully, I'll get a start on the prototype this weekend.

I've decided to screw the probe into the with a M4 thread since this suits commonly available  Renishaw probes (and I happen to have one here) . I still have yet to come up with a simple locking mechanism so a tommy-bar will have to do.

Bill
Title: Re: 3d indicator design
Post by: BillTodd on April 21, 2012, 06:53:59 PM
Interruptions, interruptions...  :bang:

only managed to get a few bits made.  Not too happy about the finish on the mounting shaft, sizes are OK but  too many rpms on the finishing pass left banded marks.

The 45° cone was easier to cut that I expected , I was able to use a tiny boring bar to enlarge and finish after a an initial cut with a 45° spotting drill.

More tomorrow...
Title: Re: 3d indicator design
Post by: BillTodd on April 22, 2012, 04:08:53 PM
Made the upper taper and lapped  it into the main shaft. The two cones work as expected :)

The two ball cages were a bit of a disaster - I forgot to change the design (PCD of the ball holes) when changed it to use larger thrust washers  :scratch:  so the balls fell out when assembled  :hammer:

Also, real world tolerances of the thrust washers  (20.7 diameter instead of 21 with a 0.2 bevel on the edges etc.) mean that the over-lap between the washers is smaller than expected, leaving the slide a little short of travel (I am aiming at 4mm in all directions). So, although I had hoped to use standard parts, I may have to make the thrust washers myself :(

Bill



Title: Re: 3d indicator design
Post by: BillTodd on April 28, 2012, 01:24:14 PM
Made the larger thrust washers from stainless steel (after three attempts!) - just need to lap the surface to a good finish.

Made the body from a piece of 40mm aluminium bar.

I still have to make the correct sized  bearing cages and the DTI mount.
Title: Re: 3d indicator design
Post by: BillTodd on April 29, 2012, 03:15:57 PM
Made the DTI mount and pressed it into the body, then spent all afternoon and most of this evening wondering why the mount hole is in the wrong place...

..slightly ironically,  given that I'm making and edge detector,  it's because I forgot to subtract 2mm from the DRO when I set the edge of the vice with the (4mm) edge detector .  :doh: :doh: :doh:

Never mind, I'll just have to bore the body 2mm deeper and reposition the cir-clip groove.
Title: Re: 3d indicator design
Post by: DaveH on April 29, 2012, 03:26:42 PM
Damn clever Bill  :bow: :bow: :bow:
 :beer:
DaveH
Title: Re: 3d indicator design
Post by: BillTodd on April 29, 2012, 03:58:43 PM
 :thumbup:

To save making two of the thrust washers, I've redesigned the slide so that the slide-tube and nut do the job (they're very lightly loaded so don't really need to be hardened). I've also found some SS mudguard washers in suitable sizes (16x50)  which will avoid having to make any more bloody washers!.

 
Title: Re: 3d indicator design
Post by: BillTodd on April 30, 2012, 04:14:11 PM
I found the time this afternoon to fix my cock-up and make the two new ball cages, so now it is almost finished.

However, I've discovered a snag with the cir-clip idea; The large thrust washer has to be held against the step in the main body if the zero reference it to be stable. The cir-clip does not hold the washer tight enough (there's no room for a spring) .

To solve that I've redesign the body to have a screwed in locking ring at the bottom. As a simpler alternative, it would be also possible to screw the washer in place with a half-a-dozen small screws.

The next problem is because everything is tight with minimal clearances, I keep getting random jams - one minute it'll slide nicely, next it'll snag and jam  - a major PITA  :bang:
Title: Re: 3d indicator design
Post by: Brass_Machine on April 30, 2012, 09:54:32 PM
Fast work Bill.

How do you plan on dealing with the random jams? Will you use any type of lubricant or keep it dry? I was thinking maybe one of the NanoLubes (http://www.ebay.com/itm/Notice-Beware-of-Counterfeit-NanoLube-on-eBay-/160780114209?pt=LH_DefaultDomain_0&hash=item256f3dd921#ht_2077wt_1297) that are always up on ebay? Dry? maybe time for some uberpolishing or will that lose too much tolerance?

Eric
Title: Re: 3d indicator design
Post by: BillTodd on May 01, 2012, 07:50:58 AM
Hi Eric,

Well, your polishing idea has helped a lot :)  (it also showed me I had a slight eccentricity in the upper taper part ) Although, I think the main problem is a poor choice of materials (aluminium is too reactive to make a good sliding material).


It is now basically working (apart from the loose main thrust washer). I'm getting about 3.5mm movement in all directions.

However, I have spotted a fundamental flaw in the design; Most of the play in the sliding parts can be removed or ignored (i.e. the ball-slide can be tight and it really does not matter if the upper taper is a bit sloppy because it is biased one direction by the forces on it). 

But, the bottom taper has to slide perfectly in the vertical direction without side play or the centre 'zero' position will be inaccurate  :bang:

Back to the drawing board...
Title: Re: 3d indicator design
Post by: BillTodd on May 01, 2012, 08:07:30 AM
Title: Re: 3d indicator design
Post by: andyf on May 01, 2012, 09:13:29 AM
Bill,

I can see the value of this device for edge-finding in X and Y, in that it enables a tool held in the spindle of a miller to be accurately located in either axis in relation to the the edge of the work, or an edge to be accurately positioned to lie along one or other axis.

But do you anticipate any use for it in the Z axis, apart from levelling the top surface of a workpiece, or tramming a milling vice? Either of those functions could be accomplished equally well with a dial indicator held vertically in the spindle.

I'm not trying to be a wet blanket; it's just that I have the feeling that I may be missing the point where Z is concerned.

Andy
Title: Re: 3d indicator design
Post by: BillTodd on May 01, 2012, 09:35:35 AM
The idea is that such a device  provides a zero reference for all axes

 I.E. One would fix the device into a holder at a known distance from the Z reference point (all the tools & holders should be set to the Z reference) then zeroing all axes can be achieved with the one device.
Title: Re: 3d indicator design
Post by: andyf on May 01, 2012, 12:56:57 PM
Thanks, Bill.

I'll have to stay with cigarette paper. I have no reliable way of setting tools to project from collets by a distance calculated from a datum which is derived from a gauge like the one you're making  :(

Andy
Title: Re: 3d indicator design
Post by: DaveH on May 01, 2012, 02:11:54 PM
Bill,

Nice video. :thumbup: :clap:

Seems to work very well  :bow:
 :beer:
DaveH
Title: Re: 3d indicator design
Post by: BillTodd on May 01, 2012, 03:37:10 PM
Quote
But do you anticipate any use for it in the Z axis, apart from levelling the top surface of a workpiece, or tramming a milling vice?

That's a good point  Andy . One quick fix for the wobbly vertical slide would be to remove it - i.e. fix the probe in to the XY-plane slide and just use it as a 2D probe  :thumbup:
Title: Re: 3d indicator design
Post by: BillTodd on May 01, 2012, 03:45:46 PM
Quote
Seems to work very well

Thanks Dave - it is, but just not quite well enough. For it to measure accurately, it has to move smoothly - it does not at the moment :( 
Title: Re: 3d indicator design
Post by: PekkaNF on May 02, 2012, 02:39:21 AM
I'm not compentent on this issue, but my first advice is not to give up. Often when all looks lost, answer is just around corner. Has happend to me many times. On some aplications I see that there is an accurate hard surface as a reference and then a member is pushed against it. Really hard to get many close fitting parts work together.

Pekka
Title: Re: 3d indicator design
Post by: BillTodd on May 03, 2012, 11:49:26 AM
Quote
my first advice is not to give up

Thanks for the encouragement  :mmr:

Adding a threaded lock nut has fixed the zeroing problem and makes the whole thing feel better :) (although I won't be using a 40tpi thread on the next one - way too fine and far too easy to cross-thread !)

Thinking about it some more; The play in the vertical slide only messes up the initial zero measurement  i.e. the rest position will not be exactly 2mm from the centre of a 4mm probe. However, as long as the play is consistent in all directions (which it should be), the edge position should be reliable.

Next , I'll make a short 4mm diameter probe  and test it.
Title: Re: 3d indicator design
Post by: BillTodd on May 05, 2012, 07:33:36 PM
Ok, a little more progress...

I've replaced the ballslide's  brass tube and washer design with a steel 'top-hat' & nut that runs directly on the balls.

The fit between the new brass bottom taper part and the ball-slide tube is now ten times better, and enlarged the top of the taper is less inclined to tip. All this has increased my confidence that this thing might work :)

I just have to tweak the depth of the shoulder in the body to suit the new parts and it should be ready to test properly  :thumbup:
Title: Re: 3d indicator design
Post by: BillTodd on May 06, 2012, 10:26:32 AM
 :(

Well it kinda works...

To test it I set it up in the 4 jaw on my lathe so I could access the accuracy using the lathe's Sony DRO (good to a few microns)

I zeroed the dial then used the DRO's touch sensor to set the DRO to zero for the 'depth' (Z axis) test. Then wound the carriage in by 2.000mm (see test1.jpg)  . The dial reading was about 50um short. This was not unexpected as I don't know how accurate the DTI is or how accurate my 45° tapers are, and absolute accuracy it is not too important for an edge detector.

Then I zeroed the DTI (at 2mm in) to test the XY plane using the cross-slide (see test1a.jog). I zeroed the cross-slide DRO just as the tool post hit the probe (couldn't get the touch sensor in a position to test this so there could be a small error) . Then moved the cross-slide in 2.000mm. This time the DTI read 80um short (meaning there is about 80um movement in the X+ direction, i.e towards the indicator, before the DTI moves) (pic test 2a.jpg).

I re-zeroed the DTI and tested it in the three other orientations (X-, Y+, Y-) see test2.jpg.  It seemed reasonably consistent  perhaps 20um out in the Y- direction (could be chucking run-out  or a gravity effect?).

All of which makes me wonder if this is ever going to be accurate enough to be useful  :doh: ?????

There is only the tiniest play in the ball slide (I chose to bond the parts together this time instead of screwing them) and the fit of the other parts would be difficult for me to improve on, so I'm now not sure if I can get this to work  :scratch:


Title: Re: 3d indicator design
Post by: Fredbare on May 06, 2012, 04:10:12 PM
I have have been following this from the beginning, and admire your skill,  and tenacity, hope you succeed, and finish this  to your high standards.

John
Title: Re: 3d indicator design
Post by: Divided he ad on May 07, 2012, 07:33:46 AM
Bill,

Sounds like you're in for a bit of "fun" testing!?

I'm sure you'll come up with something.... even if it's a good hard launch at the wall!   :bugeye:


Nah. You'll get it  :dremel:





Ralph.
Title: Re: 3d indicator design
Post by: BillTodd on May 07, 2012, 10:12:41 AM
I'm tempted to go back to my original prototype idea, which was a tipping beam. It is inherently non-linear and needs careful scaling to be anywhere near correct, but still it might be better than what I've got ATM  :scratch:

Title: Re: 3d indicator design
Post by: PekkaNF on May 08, 2012, 03:11:21 AM
I'm tempted to go back to my original prototype idea, which was a tipping beam. It is inherently non-linear and needs careful scaling to be anywhere near correct, but still it might be better than what I've got ATM  :scratch:

Three prongs/legs? Or a cunning plan to get all level and square?

PekkaNF
Title: Re: 3d indicator design
Post by: David Jupp on May 08, 2012, 05:30:51 AM
Three prongs/legs? Or a cunning plan to get all level and square?

PekkaNF

Or turn the whole thing as a profiled disc on an axle (like toy gyroscope) - an infinite number of legs better than 3 ??
Title: Re: 3d indicator design
Post by: BillTodd on May 08, 2012, 07:49:00 AM
Yes, the cross-section view can be a bit misleading.

It is, as David suggests, a disc with a torus around the edge.  :) It might  make a simple edge detector but, because to the non-linearity, it would be only be suitable to a fix sized probe


I haven't abandoned the ball slide idea just yet; While sitting on the throne this morning, contemplating the weightier of matters of state, I started to wonder where the errors are creeping in...

First up is to test the DTI. Then, just to see where the 50um/2thou" on the Z axis has gone, test the upper taper section with out the lower taper or ball in the way.

At the moment, I cannot account for all the missing 80um/3thou" in the XY plane; The play in the vertical slide  is << 1 thou" and by playing with it (pushing and pulling it ) the ball-slide has <10um according to the dial.


Title: Re: 3d indicator design
Post by: PekkaNF on May 08, 2012, 08:33:34 AM
Or turn the whole thing as a profiled disc on an axle (like toy gyroscope) - an infinite number of legs better than 3 ??
I think that accuracy needeed for that would be such that very few of us could reach it. On that front my only bet would me to use something massproduced part that has to to have that accuracy, like ball bearings and preloading them such way that clearances don't accumulate on measuring direction....which is ofcourse harder when there are many degrees of freedom on movement.

I'm really tool-envy on that lathe. Nevertheless would it be possible to double check that the measurement method and/or device does not introduce it's own set of variables. Can you affix 3D indicator on the mill or something and test 3D indicator reading agains micrometer anvill movement and possibly to verify it with a micron dial gauge or such? Even better if there were no oilfilm anywhere (spidle/slides/you name it).

PekkaNF
Title: Re: 3d indicator design
Post by: BillTodd on May 09, 2012, 10:36:27 AM
Quote
Nevertheless would it be possible to double check that the measurement method... Can you affix 3D indicator on the mill or something and test 3D indicator reading agains micrometer anvill movement
That's a good idea Pekka , and I have a 1/10000" micrometer head that would be ideal for it :)  ATM the lathe is a convenient way to quickly test bits.


I found a hour yesterday to test the DTI etc.

The DTI is OK within a few microns (i.e. within readable limits)

When I tested the Upper Taper alone. I discovered that there is a small difference (~15um) between one direction and the other. That is, going IN to zero on the DTI will give a different reading on the DRO to moving OUT to zero.

I think this is caused by the motion of the ball in the right-angle hole and this maybe due to my use of a non-flat tip on the end of the DTI, so I'll have to make a flat tip and test it.

I'm now fairly sure that the major cause of the other errors is the angle of the tapers: The upper taper shows a error of ~50um over 2mm (middle taper was cut at the same time so will have the same error) .  The lower tape was cut in something of a hurry so is likely to be even worse!

When I recover from this mystery back strain that has been giving me grief all day, I'll set up the top-slide with a sine bar and re-cut them.

Bill

Title: Re: 3d indicator design
Post by: PekkaNF on May 10, 2012, 04:05:40 AM
I am soo happy  :D you are back on track  :clap:

It happens me all the time - I'm so absorbed with the problem in my hand that I overlook procedural complications. Once I spent some time trying to figure out where the error comes from. And I was using simple DTI! Long story short: Everything I tought being square was not square and the "balls" where so small that even a little offset from theoretical measurement axis introduced error....the object was straingt but my measurement wasn't.

Spindles, bearings and slides never stop to amaze me. Move them and when you stop them they "sit". You can measure that, but they lift when you turn or mill. How on earth anything gets done with any predictability....I get massproduction, but one-offs!

PekkaNF
Title: Re: 3d indicator design
Post by: BillTodd on May 10, 2012, 03:08:42 PM
Thanks for the encouragement Pekka - it is appreciated   :thumbup:

I've fixed IN/OUT the problem with a flat DTI tip. It now repeats within a few microns.

However  :scratch: :scratch: :scratch:

I spend a couple of hours checking and rechecking my taper setting using a sine bar. Finding a stack of objects exactly 3.5355" was a challenge but,  in  the end,  two V blocks & a thrust washer measured to better than 1/2thou".

Then I carefully set the top-slide (the picture below is of the general method used ) and re-cut the tapers - well I say "re-cut" but actually there was so little difference between the existing tapers and the new uber-accurate ones it was hardly worth touching them :(

So, with my backache getting the better of me,  I set about measuring the top taper in the indicator :

Unsurprisingly; 2.000mm indicated on the DRO read 1.920mm  on the DTI   :bang: :bang:

So, where is this error? 

I then stepped the DTI 100um at a time while noting the DRO reading (see PDF)  to see it I could spot a jump or anything that could explain a taper (as shown by the difference plot)  of nearly 0.1mm (>3thou") over just 2mm (~3/32")  (that should be almost visible!)

The only place it can be, is in the right-angle hole but that doesn't look too bad from what I can see so....


what am I missing??? Ideas welcome. (remember I'm testing this without the lower taper part and ball-slide so it should be at least as good as the DTI)





 
Title: Re: 3d indicator design
Post by: PekkaNF on May 11, 2012, 06:22:56 AM
You are going to nail it big time! Every step gets you closer and closer.

I even can't cut realiably very smal DOC. I'll try to fix last cut around 0.1 - 0.2 mm depth (even though I clock it someting like 0.123 mm indicated to read the desired final dimension), othervice my parts seem to come out worse geomertically! But it's lack of my skill - no doubt.

I'm pretty damn sure your DRO and DTI reads on same axle, angular difference should be pretty large to cause error of that magnitude.

Your graph show classical scaling error that could come from incorrect aplication of metric/imperial correction on engineering of DTI or settings of DRO. I worked sometimes with SONY magnatape system and there were quite a few parameters that could be keyed in or set wrong on DIL's.

I would first check DTI against gaugeblocks to clear it. My bet would be that is the reliable one.
Then I would assume DTI fairly reliable and use same measurement range and DTI reading against lathe slide to see how much deviation is on one single axis of movement. See where DRO measures the axle and double check that you read with DTI same movement that tape/sensor sees.

Many DRO:s have many settings, not only to cobat linear erros, but also for periodical errors and sometimes error tables too, that are wonderful to have, but pain to calibrate.

PekkaNF
Title: Re: 3d indicator design
Post by: BillTodd on May 11, 2012, 07:17:54 AM
Hi Pekka,

I've checked the DTI against the DRO directly and both correlate very well (to within the thickness of the needle). I have great confidence in the Sony DRO - I have checked it against standard length gauges etc.  - It was a very expensive piece of kit when new !


I'm now thinking about increasing the bore of the right-angle hole to 8mm (as I have some 8mm bearing balls)  that should compensate for the material removed from the tapers and give me the opportunity to correct any taper (or irregularity) in the bore.

[edit]

I threw caution to the wind and drilled the hole out to 6.5mm   -  worse errors  and on close inspection there was a small step in the bore just  where the ball would be running.

Drastic action...

Dismantled the body parts completely and drilled & reamed another right-angle hole at 90° to the previous one. 

Result - less error but still ~50um short ...

Back-ache stopped play -  retired to the pavilion ...


Bill


Title: Re: 3d indicator design
Post by: DaveH on May 11, 2012, 12:40:32 PM
Hi Bill,

I really hesitated to post this, but it seem (to me) the error comes from the 45 deg taper.
The way I'm looking at it the DTI reading is always smaller, so the ball isn't moving as much as it should. So if the taper angle was larger than 45 deg that would cause the ball not to move as much.

Try a new 6.5 mm dia hole opposite the very first one, that should eliminate any slight difference to the accuracy of the main bore and the right angle hole not being exactly at 90 deg.
 
Just a thought Bill
 :beer:
DaveH
Title: Re: 3d indicator design
Post by: BillTodd on May 11, 2012, 04:08:43 PM
Quote
I really hesitated to post this, but it seem (to me) the error comes from the 45 deg taper.
Don't hesitate if you spot something ('cos I'm a blind as a bat when it come to some things)

Anyway you're kinda right ....


Cracked it :ddb:

Or rather my friend Chris cracked it  :beer:

I was showing him the problem this evening and he came up with the brilliant suggestion that the ball might not be running down the centre of the cone . BINGO Indeed it will  try to do everything in its power to avoid running down the highest spot

Any error in the centring of my hole, or play between the ball and the hole, will allow the ball to run to one side of the taper and thus run on a parabola (a conic section) not on the true 45° face.

The fix was simple: replace the ball with a small brass slide that presents a flat plane to the cone thus only following the highest part.

Testing on the lathe now shows the right-angle DTI  tracking to within a few microns (<8um at 2mm) .

I'm back on track :)

I now have to adjust the fit of the large thrust washer, so it goes a bit deeper into the body (again!) and I'll be ready to test it properly (again!)

Thanks guys, :nrocks:

 Bill

Title: Re: 3d indicator design
Post by: HS93 on May 11, 2012, 04:15:39 PM
There are some clever people on hear (and there friend's)  nice work.  :bow: :clap: :thumbup:


                                                             :ddb: :nrocks: :ddb: Peter  :ddb: :nrocks: :ddb:

                       
Title: Re: 3d indicator design
Post by: PekkaNF on May 11, 2012, 04:22:46 PM
Good job! :bow:

Hope your back-ache fades away as well.

PekkaNF
Title: Re: 3d indicator design
Post by: DaveH on May 11, 2012, 04:44:32 PM
Phew,............ I'm glad you have sorted it out Bill, I was starting to lose my beauty sleep  :lol: :lol: :lol:

 :beer:
DaveH
Title: Re: 3d indicator design
Post by: Fredbare on May 11, 2012, 05:35:13 PM
Well done Bill, excellent work.

John
Title: Re: 3d indicator design
Post by: BillTodd on May 19, 2012, 10:24:29 AM
Quick update:

I have not had to much time to fiddle with this, but following a few tests last weekend I have found the next critical bit is the ball-slide.


The ball-slide has to be tight yet slide freely for the indicator to work accurately. On this version I bonded the thrust bearing together under a  pre-load (~ 50N) using Loctite. This was fine initially but, with use, started to come loose and slightly rough.

To remove the play in the ball-slide while testing, I locked the Z axis motion using spacers and a spring washer (to pre-load the bearing again) .

The tests showed the indicator could work well - e.g. it was really quite accurate measuring the distance between two faces

However, the problem is zeroing accuracy: it does not return to 'zero' properly if moving slowly due the the roughness in the ball-slide.

Today I pressed the slide apart only  to find all the surfaces badly brinelled (dented by the bearing balls)  - I knew this could be a problem with non-hard surfaces, but was surprised because of the relatively light loads on the bearing.

So, now I'm trying to  figure out how to fit standard sized hardened thrust washers to the bearing surfaces  :scratch:


Bill
Title: Re: 3d indicator design
Post by: PekkaNF on May 19, 2012, 12:49:54 PM
The nanosecond when I saw this design, I was eyeballing these:

http://www.arceurotrade.co.uk/Catalogue/Bearings/Thrust-Ball-Bearings
http://www.arceurotrade.co.uk/Catalogue/Bearings/Needle-Roller-Thrust-Bearings

Maybe these nedle roller thrust bearing would donor hard enough discs.

You'll need preload. What kind of washer are you using? Wafer (the wavy one) or the one with fingers/prongs?

I admire your tennacy,
Pekka
Title: Re: 3d indicator design
Post by: Divided he ad on May 20, 2012, 08:27:11 AM
Fair do's Bill... You sure give a project your all  :bow:



I've missed a few instalments, but have just read through and caught up.... Top job. Hope the hardened bearing plates will cure the (final) Hurdle?   :thumbup:




Ralph.
Title: Re: 3d indicator design
Post by: BillTodd on August 26, 2012, 01:35:04 PM
We're back! Welcome to round 2...


I can't find suitably wide (i.e. large diameter with a small hole) thrust washers anywhere, so I've had to redesign the locking ring to hold a standard (30 x 17) thrust washer.

I found time today to make the locking ring and press fitted the washer. seems OK :)

Hopefully, tomorrow I'll trim the bearing cages to clear the lip (that keeps the washer square )

Bill

Title: Re: 3d indicator design
Post by: PekkaNF on August 27, 2012, 03:01:03 AM
Nice to see latest development. Does the washer mount locates only to indicator face (I assume that this surface was trued) and other surfaces are non locating i.e. clearance. Could not spot it from the design.

PekkaNF
Title: Re: 3d indicator design
Post by: BillTodd on August 27, 2012, 06:10:28 AM
Hi Pekka,

Yes, the washer sits down on a tiny facet turned true in situ (I used the indicator body to hold the ring while turning the face).

I hope to get on and finish it this afternoon (it's a bank holiday here today).

Bill
Title: Re: 3d indicator design
Post by: BillTodd on August 27, 2012, 02:55:31 PM
Well, it's back together. Seems to centre to zero pretty well. There's a tiny bit of dead space ~20um ( from some angles and not others, which is a bit odd ) .

It has just over 3.5mm movement in all directions which is pleasing, since that's more than the previous set-up gave. The 45° slide still feels a little rough (need to be run in).

I'll try to find the time to test it tomorrow .

Bill
Title: Re: 3d indicator design
Post by: AussieJimG on August 27, 2012, 07:17:30 PM
This is an enthralling thread. I have been watching in admiration of you Bill, for your initiative in starting this project and your determination in pursuing it.

It is really wonderful to watch you track down the errors and modify the design and to see the interaction and assistance from others, particularly PekkaNF. Thanks to all of you.

Jim
Title: Re: 3d indicator design
Post by: BillTodd on August 28, 2012, 04:21:04 PM
:) Thanks Jim.

This afternoon I just got the thing in the lathe to test it when a mate turned up with a dead motor.

His swimming pool pump had eaten its own bearings (again!)  -

'it smells like the motor's dead to me' -  I said,  :smart:

'no, it's been running fine'

two hours later, after making a sleeve to fit the new bearing on the knackered shaft, we had the motor running....

for about three seconds !   :doh:

Verdict:  new pump required

Will try again to get the indicator tested tomorrow :(
Title: Re: 3d indicator design
Post by: BillTodd on August 29, 2012, 01:08:10 PM
Between phone calls, I manage to do a quick test to see how well the indicator works between faces...

Hmmm quite well, but consistently 17thou off (measuring an inch)  - I was expecting an error because of the dead spot in the middle (slack in the ball slide & other parts) but not that much   :bugeye:

However, it is consistent, giving the same error in all directions (well the 90, 180 etc. that I tested) so it's a simple matter of adjusting the size of the probe to compensate...

That's where the day peaked  :hammer:

Had a phone call - "This 'clip' you want made... Is it really nearly an inch thick and half-a-metre wide ???"

DXF conversion strikes again - 16mm gets changed to 16 inches then converted back to 406mm on import   :bang:

I make the probe tip, after a lot of faffing around

Then I manage to break the  washer out of the ring while trying to screw the probe in  - Of course,  it will not go back in with out more faffing - Now I'm waiting for the loctite to set...  :bang:

Time for more coffee
Title: Re: 3d indicator design
Post by: BillTodd on August 30, 2012, 04:17:43 PM
Arrrgh...  :bang:

Finally I found time to do some tests.  I clamped a micrometer in the tool post and used the DRO's touch probe to give me an absolute zero face  then adjusted the mic to give a second face at 20mm spacing.

 :scratch:

While it appears reasonably consistent in any one direction ( i.e. once zeroed in a direction it will return to zero within 10um - even if removed from the lathe),  it will not accurately measure between faces because of the play in the bottom taper slide (I had to re-ream this after I threaded it, so I guess it's now too big :()

Maybe it's time to throw in the towel ? (I've lost faith in the design)

Bill

Title: Re: 3d indicator design
Post by: PekkaNF on August 31, 2012, 04:04:23 AM
..
While it appears reasonably consistent in any one direction ( i.e. once zeroed in a direction it will return to zero within 10um - even if removed from the lathe),  it will not accurately measure between faces because of the play in the bottom taper slide (I had to re-ream this after I threaded it, so I guess it's now too big :()

Maybe it's time to throw in the towel ? (I've lost faith in the design)

Bill
The toublemaker...is it part "lower taper"on picture at your Reply #53 on this page? Would making a new one rectify this problem? Or are you this feeling of uncertainty, when one thing gets fixed and then another chalenge manifestes itself?

To me more changing part looks  "upper taper" . Is it guided on the double tapper end (I mean the narow end that has a taper on both sides) or at far end? You are working on acuuracies and geometries that are pretty chalencing. To me it looks like you wanted to make this probe as short as possible and that will produce fairly narow land on this double taper end which looks to me like very important guide.

I think that the basic design is sound, it just needs some tweaking to get it Goldilocs right.

What is that professional looking probe on upper picture?

Pekka
Title: Re: 3d indicator design
Post by: BillTodd on August 31, 2012, 03:46:14 PM
Quote
The toublemaker...is it part "lower taper"on picture at your Reply #53 on this page?

No, the problem is the vertical slide part of the ball-slide., when I threaded the part is shrunk slightly.  I had to re-ream it , (which I made a hash of) and now it doesn't fit as well.

Quote
To me more changing part looks  "upper taper" . Is it guided on the double tapper end
Yes, I know what you mean. My hope was that the DTI spring would force it to one side thus reducing the error caused by the slack.

Quote
I think that the basic design is sound,
sound maybe, but not good - it is too reliant on near-perfect sliding joints -  Like the case of the 'upper-taper' above, it started off a very good fit, but as the device was polished and used  the fit became worst - to the point of not being accurate enough.

I'll have another look at it over the weekend, but I have a lot of work coming up, so the 3d probe will have to go on the back burner if it isn't abandoned.


Quote
What is that professional looking probe on upper picture?

It's a Sony TS1 touch probe - It plugs into the back of the Magnascale DRO allowing it to locate to a couple of microns (it says in the manual!)  - It really just a 10mm ball (on a spring) . When it makes contact with ground (machine/earth) it completes a circuit that tells the DRO to bleep (in an annoyingly loud way)

Bill
Title: Re: 3d indicator design
Post by: BillTodd on February 28, 2015, 03:28:32 PM
Time to revive a 2 1/2 year old thread....

Dug the old prototype out again the other day and began wondering if the design could be rescued  - having set it up in the mill , it didn't seem as bad as I had led myself to believe, so started thinking again .

The main problem with the design is its (over?) reliance on sliding joints , so improving these seems like a place to start

The upper taper can be made self-adjusting by adding a  floating taper part which expand a new springy upper taper (or at least that's the theory)

more later...
Title: Re: 3d indicator design
Post by: BillTodd on March 01, 2015, 01:30:25 PM
Well made the floating taper part. Turned the taper in the existing upper taper to fit the new part then try to cut the slots in it... all the time i'm thinking - make a fixture ,  make a fixture then bang -  end of part one :Doh:


2 hours later I have another upper taper made and, this time a fixture to hold the taper while slotting.

Troble now is the new part is tight and needs to be 'run in' ... Sometime this week I'll pop it in to one of the bridgeports at work and see if it has improved any.
Title: Re: 3d indicator design
Post by: Manxmodder on March 02, 2015, 01:05:27 AM
Bill,I hadn't seen this thread before now,that's a really fine piece of prototyping work and I'll be watching with interest......OZ.