Author Topic: Experiment Engraving Machine Dials (Read 23362 times)

awemawson · « **on:** February 21, 2016, 07:08:09 AM »

This barely qualifies as a project - just a bit of experimentation.

I wanted to add a calibrated dial to the infeed screw of my Dormer 108 Drill Sharpener - later models have it and it's a relatively simple and worthwhile addition. So I just need to engrave lines and numbers around the circumference of a doughnut of steel.

Recently having bought CamBam (very impressed for the money) I drew up a linear version of the scale from which to generate G code

awemawson · « **Reply #1 on:** February 21, 2016, 07:18:03 AM »

Now available with CamBam is a 'plugin' that enables you to 'wrap' G code around a cylinder. You specify the cylinder diameter, the angle you need to wrap around, and it does the maths to convert all the (in my case) Y axis moves into appropriate angles for the A axis to move - (there are several programs 'out there' on the web that do the same).

As original this plug in wasn't quite suitable in that it generated too many decimal places after the point (5), and embedded comments in brackets - neither of which are acceptable to my Heidenhain TNC355 control which chokes on more than 3 decimal places in metric mode. The nice author of the plug in tweaked it so the latest version on the CamBam site now has a box to tick to supress comment, and a selection for the precision ie figures after the point

So now we need something to engrave. It just happens that I had a length of 2" 'hollow bar' amongst my 'come in useful' bits - so a slice was cut off, bored to 30 mm i/d and skimmed to 50 mm o/d

awemawson · « **Reply #2 on:** February 21, 2016, 07:26:14 AM »

Now the eagle eyed amongst you will notice that I'm using a 3 jaw chuck - should really be a 4 jaw to get it spot on - in practice the mandrel run out was only a couple of thou, and this was an experiment rather than the finished item, so it was the three jaw

The mandrel set is rather nice - can't remember where it came from but was made by the Armature Manufacturing Co of Oldham - no doubt they don't exist any more

They have a taper sliding arrangement that expands and grips a hole in the part, and you press them in to expand, then tap them with a soft hammer to release.

So it was duly mounted in the 4th Axis on the Beaver Partsmaster, a few careful setting made to origins and I had at it with my diamond engraver

awemawson · « **Reply #3 on:** February 21, 2016, 07:32:06 AM »

Now it started off really nicely - sharp cutting - crisp engraving - then it all went down hill

Turned out that I'd lost the tip of the diamond

... no spare

So I decided to pull it out of the 4th axis - skim a few thou off and start again with my air turbine powered rotary engraver with a 90 degree carbide cutter running at about 20,000 rpm.

This went ok but the engraving width is too wide and nothing like as nice as the diamond drag engraver produced - replacement diamond on order

awemawson · « **Reply #4 on:** February 21, 2016, 07:33:33 AM »

Now contrast that engraving with a bit I did as a test earlier - nothing like as nice

awemawson · « **Reply #5 on:** February 21, 2016, 07:41:45 AM »

It's been a useful exercise in that I've learned a few things :

... diamonds don't conduct electricity so no use trying to use my LED 'Z Height' setting gauge to set tool length

... I must have used ceramic bearings in my air turbine all those years ago - the spindle & collet are electrically isolated from the body so again no point in trying to use the LED Z height gauge !

... my lubrication / misting system for the air turbine that passes oily air through the bearings to keep them alive works, but using WD40 is messy and needs refining somehow

... my HUGELY expensive Heidenhain TS511 automatic probe does (JUST!) clear the 4th axis tailstock in use on automatic tool changes without breaking it's nifty little ruby precision ball off

When the diamond arrives I'll make another one - but it's been a learning exercise

So where does this dial go - here:

philf · « **Reply #6 on:** February 21, 2016, 08:11:48 AM »

Andrew,

I'd forget the diamond and use tungsten carbide for most materials. I chipped my diamond (forgot to set Z zero!) and thought I'd try a point ground onto a broken carbide end mill. I've never had to regrind it and I've done a lot of engraving with it - much on to stainless.

I've got plenty of 1/8" shanked broken or worn out cutters so I can grind up different angles for different hardnesses. (They can also be ground into rotary engraving tools but that involves a lot more work.)

Drag engraving doesn't seem to take paint or filler as well as rotary engraved. Maybe because it's very shallow and the surface finish in the engraving is too smooth.

My diy tool height setter doesn't rely on conductivity and works very well.

Cheers.

Phil.

awemawson · « **Reply #7 on:** February 21, 2016, 11:06:23 AM »

Phil, thanks for that tip

So encouraged by your suggestion I steamed up the Clarkson T&C grinder, found a green grit wheel and modified a broken 1 mm carbide end mill that had a 3.17 mm shaft.

That completed I made another steel doughnut, went through the origin set ups again (LED sensor OK on carbide

) and engraved the new disk.

Oh so much better than the rotary engraver, but obviously shallower. I need to experiment with tip angle - this one was about 40 degrees included angle as far as I can measure - and was completely arbitrary.

I suppose the sharper I make it, the deeper it will cut but the more likely to break

philf · « **Reply #8 on:** February 21, 2016, 11:36:33 AM »

Andrew,

I usually use a 90 degree included angle on hard materials and 120 degree on soft. You may find that 90 degrees will give you a wider mark than 40 even at the same pressure although I've not done any scientific comparisons varying angle and pressure vs width of mark.

This example was a test in a piece of brass before I risked it on a trophy.

Have you got some backlash in your dividing head? In the 4th image the gap between 50 and 51 looks smaller than the rest. Or is it an optical illusion?

Phil.

awemawson · « **Reply #9 on:** February 21, 2016, 11:47:56 AM »

I'll do some experiments. I've no idea what the steel is that I was engraving, but it's certainly not plain mild steel. Cleaning up after boring, my normal de-burring tool wouldn't touch it - I think that it had work hardened - or maybe it was pre-hardened stock

mattinker · « **Reply #10 on:** February 21, 2016, 12:44:05 PM »

That was nice to see! I think it counts as a project.

Thanks Andrew, regards, Matthew.

BillTodd · « **Reply #11 on:** February 21, 2016, 01:08:42 PM »

Snap Matt,

very interesting :-)

what about grinding the carbide to a sharp V D bit? (as used in the gravograph engravers)

Bill

philf · « **Reply #12 on:** February 21, 2016, 01:35:27 PM »

Quote from: BillTodd on February 21, 2016, 01:08:42 PM

Snap Matt,

very interesting :-)

what about grinding the carbide to a sharp V D bit? (as used in the gravograph engravers)

Bill

Bill,

I've done just that for my PCB isolation routing cutters.

The most difficult part is grinding the carbide to half the diameter. A diamond wheel helps considerably.

I found a useful webpage with clearance angles for different materials:

http://www.pilotltd.net/engraving.htm

Phil.

awemawson · « **Reply #13 on:** February 21, 2016, 03:06:00 PM »

Have you got some backlash in your dividing head? In the 4th image the gap between 50 and 51 looks smaller than the rest. Or is it an optical illusion?

Phil.

Well spotted Phil - I hadn't noticed that

When I first drew the scale I'd intended to have it read 50-0-50 and started drawing the lines at the middle out to +50 then back to the middle and out to -50. I then changed my mind and re-numbered them 0-100 (well 0-0 really as the 100 corresponds to 0)

When the program generated tool paths and G code it did so in the order that I drew the individual entities, so started in the middle to +180 degrees, then back to the middle and out to -180 degrees. This later version of CamBam allows you to optimise the cutting order, which I've now done so it engraves all the lines going clockwise, then re-winds and engraves all the numbers clockwise - so cutting will all be in the same direction and backlash eliminated. It does beg the question though why doesn't it show in the numbering, as any one number is being cut in both directions. It is just possible that the figure "0" on all the numbers has a more curved left side than right side, but the difference is nothing like that between the 50 and 51 lines that you pointed out.

At least my final version should be uniform. Nice to get it right, but in this application it doesn't matter a jot - the feed screw dial is 'zeroed' when one cutting edge of the drill is sharpened, then backed out and returned to the same zero for the other cutting edge. The scale calibration is just to show how far you have to go to zero.

Just shows - this is all a useful learning exercise

RotarySMP · « **Reply #14 on:** February 22, 2016, 05:11:22 AM »

Did you grind a number of facets on that 1/8th Inch carbide or is it conical with half ground away?

Mark

awemawson · « **Reply #15 on:** February 22, 2016, 05:48:52 AM »

Mark, the last version that you saw was 'drag engraved' ie the cutter was not rotating and was just a 40 degree conical point pushed and pulled across the work. In the earlier example I used a high speed rotary engraver with a commercial carbide 'D bit' engraver which is 90 degree included angle.

RotarySMP · « **Reply #16 on:** February 22, 2016, 10:15:14 AM »

Thanks. Looks really nice.

Mark

awemawson · « **Reply #17 on:** February 23, 2016, 06:23:16 AM »

The more I look the more I find

Watching the machine engraving another version I was looking at the displayed angle of the 4th axis incrementing away - 100 divisions over 360 degrees so why is it incrementing by 3.575 degrees and not 3.6

So I looked at the G code that it was obeying, and sure enough if you look at the difference between successive values for A they are 3.575 degrees apart as you can see in the attached file of G code

awemawson · « **Reply #18 on:** February 23, 2016, 06:28:44 AM »

Much head scratching ensued

Much coffee consumed

But it wasn't until a period of awakeness at 3 o'clock this morning that it dawned on me. The wrapping program works out the extents of the code that it is wrapping in terms of maximum X and Y then applies it's clever mathematics. The lines to be engraved are fine and in the right places BUT THE ZERO DESCENDS BELOW THEM

This means that the length of the wrap is wrong as half of the width of '0' is added to the Y length as you can see in this picture:

awemawson · « **Reply #19 on:** February 23, 2016, 06:31:11 AM »

The solution is trivial. add some lines below the zero, remove some lines at the other end of the scale and all should be hunky dory.

As per these pictures:

awemawson · « **Reply #20 on:** February 23, 2016, 06:34:39 AM »

So now the 'length of the wrap' is dictated by the lines and not the numbers - so did it work?

... well I've not cut metal to prove it, but if you look at this version of the G code you'll see that the A values are incrementing now by 3.6 degrees. 100 x 3.6 = 360 = one revolution which is what it should have been all along.

... as I've said before, it's a learning exercise - and I'm certainly learning things that I wouldn't previously have considered

raynerd · « **Reply #21 on:** February 24, 2016, 02:48:29 PM »

Cracking post Andrew, learnt a lot. I may invest in cambam and will be trying the carbide pointed engraver. I currently use a diamond but I see the carbide works well.

Chris

DavidA · « **Reply #22 on:** February 25, 2016, 07:20:02 AM »

Andrew,

I was really surprised when I read your line stating that diamond doesn't conduct electricity.

So surprised I looked it up. And it seems..

...The electrical resistivity of most diamonds is on the order of 1011 to 1018 Ω·m...

That should read 10E10 to 10E18 Ohm per square Cm.

As diamond is carbon and carbon is used in conductors (Brushes etc) it was unexpected.

We learn something new every day.

Dave.

awemawson · « **Reply #23 on:** February 25, 2016, 08:57:40 AM »

ARGH I Have a PROBLEM

I've been chasing tiny errors in the engraving line spacing for what seems ages - convinced I got the wrapping program set wrong, or something in my original drawing like too many or too few lines, so in desperation I decided to to a manual test:

a/ I skimmed off one of the 'doughnuts' to 48.5 mm o/d and mounted it up on the 4th axis

b/ I sent the 4th axis to -10 degrees, then to 0 degrees to eliminate any back lash

c/ I then manually drove the engraver into contact and scribed a line then raised it again.

d/ I then drove the 4th axis to 360 degrees then manually drove the engraver into contact and scribed a line then raised it again.

e/ I then drove the 4th axis to 720 degrees then manually drove the engraver into contact and scribed a line then raised it again.

f/ I then drove the 4th axis to 1080 degrees then manually drove the engraver into contact and scribed a line then raised it again.

Now all those lines that I scribed SHOULD fall on the same place and over lay each other BUT THEY DON'T

As you can see there is an increasing cumulative error. To try and quantify it the gap between lines is of the order of 0.833 mm on a circumference of 152.367 (Pi x 48.5) so of the order of 0.833 x 100 / 152.367 or 1/2 % which is far too large to tolerate !!!

Back lash has been eliminated by travelling in the same direction all the time so what the heck could cause that

BillTodd · « **Reply #24 on:** February 25, 2016, 09:38:58 AM »

Your 4th axis settings must be wrong too many (or too few ) pulses/steps per rev. (has someone swapped encoders by any chance) . What make of 4th axis BTW?

awemawson · « **Reply #25 on:** February 25, 2016, 10:00:18 AM »

Bill it's a long story but covered in depth here:

http://madmodder.net/index.php/topic,9439.0.html

The axis is travelling too far - the only possibilities that I see are:

a/ gear ratios wrong (seems very unlikely)

b/ obscured 'gap' in encoder disk so loosing one or more pulses per rev.

I was about to delve into that thread on building the 4th axis to refer back to the ratios to see if b/ is mathematically likely

awemawson · « **Reply #26 on:** February 25, 2016, 11:21:29 AM »

OK so the encoder is 125 counts per rev
It is tooth belt driven by the servo motor 20:25 reducing the count to 100 per servo motor rev
The servo motor is geared to the worm gear 4:1 in a low backlash set up
The worm to the worm wheel is 90:1 - again low back lash set up

so 90 x 4 x 100 is 36,000 encoder pulses per axis rev

Now to be out 1/2% seems very strange unless the worm / wormwheel isn't exactly 90:1 and I can't believe Nikken would make something with an odd ratio - it was originally a stepper motor driven rotary axis with the same 4:1 gearing

0.5% (approx) is 180 steps being lost if that's the cause

... I'm befuddled - none of this makes sense

Short of pulling it apart and physically checking each ratio in the drive chain accurately I don't see a way forwards

(I re-did the test and it is absolutely consistent, so unlikely to be a loose coupling or something like that - I also, having run forwards 3 revs to 1080 degrees, ran back to -10, then forwards to zero and it was bang on)

John Stevenson · « **Reply #27 on:** February 25, 2016, 12:02:16 PM »

PM or email your address aGain [ best Forrest Gump voice ] and I'll stick another 125 count Heidenhain encoder on the carrier for you.
That should then take one option out of the scenario [ unless this encoder is pants as well ? ]

RussellT · « **Reply #28 on:** February 25, 2016, 12:21:48 PM »

The worm can't be out by half a percent - the wheel would need a half tooth. If it was consistently missing one gap in the encoder disc it would be out by 0.8 percent - but could it miss one gap about 60 percent of the time.

Can you try it with slower movement and see if that's the same?

Russell

BillTodd · « **Reply #29 on:** February 25, 2016, 02:22:43 PM »

does the Heidenhain encoder have a zero output? (i know some do )

Can you confirm using the zero output that you are getting 125 counts per rev ?

awemawson · « **Reply #30 on:** February 25, 2016, 03:32:52 PM »

Bill, no I don't think that this one does

Anyway the plot thickens

I wanted to prove if the error was actually consistent, and measure it more accurately. So I set up a 'zero pointer' (*) and wrote a diddy program to turn the 4th axis 20 turns or 7200 degrees so that the error would be magnified and more easily measured.

Odd results: first two runs at 2000 degrees per minute gave errors of 37 and 38 degrees added to where we should be - so close that I thought that I'd perhaps bumped the scriber holder when taking the picture.

But I then repeated the test of 7200 degrees but halved the speed to 1000 degrees per minute, and got a result of 31 degrees

... so it's NOT consistent and could well be a dim bulb in the encoder (I think that they use an under run pea bulb) or it could conceivably be a pulley or shaft slipping.

A bit of dismantling tomorrow if I can find time

Turns out to be about 0.527% so the original guess at 1/2% wasn't too far off

(* I'd have used the inbuilt fidicule marker if I'd remembered that there was one

)

John Stevenson · « **Reply #31 on:** February 25, 2016, 05:45:51 PM »

It's probably on last years British summer time.

Encoder leaving here on Saturday, clearly marked "Please throw underarm "

awemawson · « **Reply #32 on:** February 25, 2016, 05:50:13 PM »

John you are a hero

awemawson · « **Reply #33 on:** February 26, 2016, 06:54:28 AM »

so bright and early this morning I set it going at a crawling 100 degrees a minute for the 7200 degree test, then went and cleared out the pigs, cooked my porridge, ate it, and returning to the workshop it was ALMOST there

(an hour and 12 mins of course)

... how did it do, well it still over travelled but by less at 29 degrees.

So no choice but to start pulling the thing apart, a diversion I could well do without. Swarf cover off, and even so getting the end cover off the belt drive was a pain ... who designed this ....

(me!)

Eventually got the bits obscuring the belt cover off to reveal a toothed pulley on the end of the servo motor with a grub screw only finger tight

I was tempted to put the pulleys back with Loctite as well as grub screws, but future dismantling would be almost impossible without destroying the alloy pulleys.

So I decided to drill and tap them both for a second grub screw at 90 degrees to the first - this is where things started to go awry

Trying to undo the (hard of access) grub screw on the encoder, the ball end of my (cheap and nasty Chinese) ball ended allen key decided this was the time to break off inside the grub and jam there forever

However I managed to gently tap the pulley off the shaft, then as the grub screw / broken ball end proved too hard to drill out, put two new grubs in and ignored the old one. I put a reamer through to take the slight protrusion of the old grub screw which would have stopped the pulley going back on.

(These are tiny M3 grubs with 1.5 mm hex sockets so a bit delicate.)

So having jumped through those hoops it was just a case of putting it back together making sure the pulleys were aligned and the belt tensioned and trying it out.

..did it work .....

...you bet

SORTED

Now perhaps I can get back to making that bally dial that revealed this issue

John Stevenson · « **Reply #34 on:** February 26, 2016, 07:55:54 AM »

Clumsy bastard.

Still sending the encoder as it's no good to me

awemawson · « **Reply #35 on:** February 26, 2016, 08:36:59 AM »

Thanks John, you're a brick

awemawson · « **Reply #36 on:** February 26, 2016, 09:17:39 AM »

So with no more ado I skimmed that doughnut down yet again (48 mm now!), set the mandrel in the 4th Axis and had yet another go.

... hoo blooming ray ... it worked perfectly. The scale wraps around the part seamlessly (the join is between the 95 and 96 lines, and I suspect that the characters are better formed - one side of the zero's previously looked a little straight.

So now I can go ahead and make the real thing complete with recesses for O rings to add friction in place on the drill grinder

Pete W. · « **Reply #37 on:** February 26, 2016, 10:06:13 AM »

Hi there, Andrew,

I'm pleased to read that you've got it sorted.

John Stevenson · « **Reply #38 on:** February 26, 2016, 10:21:43 AM »

Nope, 96 is greater than 97.

[ Should have gone to specsavers ]

Spurry · « **Reply #39 on:** February 26, 2016, 11:16:17 AM »

Andrew
Very interesting write-up; I am pleased that it was you sorting out the problem...not me.
Pete

mattinker · « **Reply #40 on:** February 26, 2016, 11:40:49 AM »

You were wondering whether this qualified as a project? Had us on tenterhooks for days!!

Glad it worked out, all the best Matthew.

SwarfnStuff · « **Reply #41 on:** February 27, 2016, 01:56:56 AM »

Not only kept us intrigued but it is always good to hear of a successful outcome where swarf, sweat and head scratching finally win out.

Gives us all hope that we too will get there eventually.
Now if I can only find where the workshop gremlins put that part I was working on a few minutes ago I too might have a win.

Thanks for a good read,

John B

awemawson · « **Reply #42 on:** March 04, 2016, 07:59:45 AM »

John S, Many thanks

Spare encoder arrived this morning - much appreciated

dawesy · « **Reply #43 on:** March 04, 2016, 03:18:33 PM »

Glad this is sorted. Always good when you get to the bottom of an annoying problem

John Stevenson · « **Reply #44 on:** March 04, 2016, 07:02:56 PM »

It's not sorted though.
Seriously 96 is greater than 97, look at the picture.

awemawson · « **Reply #45 on:** March 07, 2016, 10:37:24 AM »

John I agree that that version looks slightly unequal. Not sure why

May be that the drag engraver, which is used non-rotating, turned a bit - it won't be exactly concentric due to the screw holding the bit, and 97 was the first line engraved, and 96 the last.

I gave up with drag engraving as the depth and definition wasn't sufficient, so I dug out my 'Tapmatic Speeder' that gives a 6:1 speed increase on normal spindle speed, and engraved the dials using a conventional carbide 'Vee bit'. I've been putting off using it, as it requires a 'reaction bar' to stop it's body rotating, which was a bit of a pain to arrange.

So here they are temporarily mounted on the drill grinder - I'll clean them up and nickel plate them when I've enough bits waiting for plating for it to be worth setting the tank up.

vtsteam · « **Reply #46 on:** March 21, 2016, 10:14:33 AM »

Very enjoyable and useful reading, Andrew!

John Stevenson · « **Reply #47 on:** March 21, 2016, 11:28:46 AM »

I have been doing some rotary engraving using a diamond drag over the weekend.
Quite tiny letters in brass for something the Delectable Debs ™ ® © sells, This is new though as up until now she just stamped the model on with 1/8" stamps which was all she had, but now she has her own CNC, once perfected I can pass the job over.

Sooner than hi-jack Andrews post ' again ' I'll start a new one tonight after work.

awemawson · « **Reply #48 on:** March 21, 2016, 11:30:48 AM »

Hey what's a friend for if he can't hijack your thread

John Stevenson · « **Reply #49 on:** March 21, 2016, 11:54:57 AM »

OK quick teaser.

Quite hard to photograph being shiny brass and so small.

The brass bar where the letters are is 8mm in diameter and the capital letters are 2.3 mm high.

More later tonight with the tool.

News:

Author Topic: Experiment Engraving Machine Dials (Read 23362 times)