Author Topic: Coax indicator design  (Read 55230 times)

Offline BillTodd

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Re: Coax indicator design
« Reply #25 on: November 08, 2010, 02:26:31 PM »
Rocker on  :headbang:

Managed to get the slot cut and the rocker made.

I was wondering how to grind the involute curve on the tips of the rocker when this idea struck...

I stuck a disc of emery to the bottom of the indicator body, assembled the lot into the lathe chuck, then ground the tips in situ :)

Bill

Offline BillTodd

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Quickly centring a rotab
« Reply #26 on: November 08, 2010, 02:35:24 PM »
I thought you might like to see how I quickly centre my rotary table.

I found a expanding clamp, the type used to fix pulleys to shafts, that conveniently fits the MT3 hole in my rotab and fits the 10mm end of my little edge detector.  

I can pop the clamp in to the hole in the rotab, lower the edge detector in to the clamp, nip it up finger tight, then by either sighting or feeling the two parts of the edge detector , I can align the centre to about 1 thou" or so.
« Last Edit: November 08, 2010, 02:39:01 PM by BillTodd »
Bill

Offline RichardShute

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Re: Coax indicator design
« Reply #27 on: November 08, 2010, 06:48:17 PM »

Quote from: Richard
Looks like you are making a nice job of it Bob.
I'm sure Bob will make a far better job of it than I ever will :)


Bill
Bugger! Well I knew who I meant, just a keyboard problem. Appologies...

I'll nut out some sketches of some sort for interest, maybe for the Mk2.

Richard 
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Offline BillTodd

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Re: Coax indicator design
« Reply #28 on: November 09, 2010, 03:52:45 PM »
Almost ready to test...

Made the little probe holder this evening. The plastic wheel in the photo will be replaced later with a lever (I think).

Bill

Quote
I'll nut out some sketches of some sort for interest, maybe for the Mk2.
Sounds good :)

John, Does your Blake device have a spring to bottom the body, or does it, like mine, rely on weight?
« Last Edit: November 09, 2010, 03:56:00 PM by BillTodd »
Bill

Rob.Wilson

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Re: Coax indicator design
« Reply #29 on: November 09, 2010, 04:23:07 PM »
Hi Bill

I like the way you ground the tips  :med:  ,,,,,,,,, looking forward to seeing it in action  :thumbup:


Rob

Offline BillTodd

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Re: Coax indicator design
« Reply #30 on: November 10, 2010, 02:54:07 PM »
Well that seems to work OK  :)

Made a little screw to clamp the probe onto the rocker (worked at second attempt having bent the first one  :hammer:)

Made a simple hook using a 3mm rod and a magnet from a small loudspeaker to hold the indicator still. Then, gave it its first test...

http://www.youtube.com/watch?v=wQYw0c3RN_0

There's a residual ~1/2 thou" wobble caused, I think, by the face out of alignment with the bore. The facing had to be a second operation because of the dual diameters of the bore - I may have another go at it, taking more care this time (MkII will have a straight bore) .

I also noted a tiny 'kick' with the thing zeroed on the mill, the cause of which I have not been able to find - could be a piece of **** in the taper part or ???

Bill



Bill

Offline andyf

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Re: Coax indicator design
« Reply #31 on: November 10, 2010, 03:27:39 PM »
That's terrific!
:clap: :clap: :clap: :clap: :clap:

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline bp

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Re: Coax indicator design
« Reply #32 on: November 10, 2010, 04:11:47 PM »
Excellent!!
cheers
Bill Pudney
Adelaide, Australia

Offline j45on

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Re: Coax indicator design
« Reply #33 on: November 10, 2010, 04:26:54 PM »
Very nice job  :bow:
Jason

Rob.Wilson

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Re: Coax indicator design
« Reply #34 on: November 10, 2010, 05:45:11 PM »
JUST THE JOB , nice one  :bow: :bow: :bow: :bow:

Rob

Rob.Wilson

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Re: Coax indicator design
« Reply #35 on: November 10, 2010, 05:52:34 PM »
 :offtopic: but just a thought  ,, i was thinking of using the ball from  piercing barbells for the end of the probe ,, they are stainless steel , come in a range of sizes and have a threaded hole  :med:  ,
http://en.wikipedia.org/wiki/File:Piercing-Barbell.jpg

Rob

Offline bp

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Re: Coax indicator design
« Reply #36 on: November 10, 2010, 08:16:30 PM »
Somewhere for a similar application, I'm pretty sure that I've seen someone using balls from ball bearings sat in a little recess, retained by Araldite, or Loctite.  Could even soft solder them, the temperature wouldn't be high enough to affect the hardness of the balls.  Balls are available from bearing stockists at an amazingly low price for such a precision item.
Cheers
Bill Pudney
Adelaide, Australia

Offline Divided he ad

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Re: Coax indicator design
« Reply #37 on: November 10, 2010, 10:40:17 PM »
Bill....  :jaw:  :bow:  :bow:  :bow:  :beer:


Well, that's just great (not sarcasm) made with pace too!  0.5 thou wobble!!! Not a bad tolerance for the prototype eh?


Very impressed  :clap:





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Offline Brass_Machine

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Re: Coax indicator design
« Reply #38 on: November 10, 2010, 11:27:39 PM »
Wow.  :bow:

Not only does the prototype work fairly well, it looks fantastic. Looking forward to MK2

Good job sir

Eric
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Offline Bogstandard

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Re: Coax indicator design
« Reply #39 on: November 11, 2010, 12:43:02 AM »
Bill,

Methinks you've got it nailed.

Very well done.

I honestly don't think you need to make a Mk 2, just turn up a close fitting internal mandrel and gently skim the end of Mk 1. You should only be removing about a thou, so a tiny spot of superglue should hold it.

BTW, you have really shown with your vid how easy these tools make setting up finding centre really is. It used to take me ages to do it the normal way with a DTI, even the act of turning it by hand used to deflect the needle slightly, my coax tool was a true revelation when I first started to use it.


Bogs
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Offline sbwhart

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Re: Coax indicator design
« Reply #40 on: November 11, 2010, 01:35:18 AM »
Great work Bill.

I've got a trade bought Coax and its a bit on the long side for my machine I had to make a special collet to get it fitted, but this design being shorter would be a lot more convenient.
 
:clap: :clap: :clap: :clap: :clap:

:thumbup: :thumbup: :thumbup: :thumbup: :thumbup:
 

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Offline BillTodd

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Re: Coax indicator design
« Reply #41 on: November 11, 2010, 04:58:37 AM »
Thanks Guys  :D

Rob, I like your bar bell idea - It'd save me having to rig up a ball turner.

bp, Another good idea - The ends of my other indicators have a ball in a pocket as you suggest.

Bogs, I like the mandrel idea. I don't need to face all the way to the centre, so I can set the thing between centres.

The aim of a MkII version would be simpler/easier construction and/or more accuracy. I have yet to test the centring with another DTI but judging only by the feel of the handles it no better than +/- 1 or 2 thou"; There's about a 3:1 loss between the probe/rocker and the DTI so 1 thou" on the indicator could be 3 at the work piece.

Bill
Bill

Offline kwackers

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Re: Coax indicator design
« Reply #42 on: November 11, 2010, 07:59:17 AM »
Bill,

I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?

(Nice job btw!)

Offline slowcoach

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Re: Coax indicator design
« Reply #43 on: November 11, 2010, 11:51:27 AM »
Brilliant  :clap: :clap:

Rob  :thumbup:

Offline BillTodd

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Re: Coax indicator design
« Reply #44 on: November 11, 2010, 12:38:48 PM »
Bill,

I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?

(Nice job btw!)

ATM 10thou" of displacement caused and indicated 3 thou on the DTI (which would be doubled as run-out). I suppose a quick improvement would be to swap the cheap DTI for a tenths indicator.
« Last Edit: November 11, 2010, 02:16:03 PM by BillTodd »
Bill

Offline winklmj

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Re: Coax indicator design
« Reply #45 on: November 11, 2010, 01:59:48 PM »
Amazing...design to Mk1 in 6 days. I want one.
Mike

Offline BillTodd

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Re: Coax indicator design
« Reply #46 on: November 11, 2010, 04:34:45 PM »
Ok here's the MkII provisional design

A straight shaft should be easier to make and means the critical parts of the body, the bore and face, can be machined in one operation.

Bill

« Last Edit: November 11, 2010, 04:38:31 PM by BillTodd »
Bill

Offline mklotz

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Re: Coax indicator design
« Reply #47 on: November 12, 2010, 01:07:45 PM »
Bill,

Can I encourage you to provide a few measurements for your design, please?  Just the main shaft and the bronze sleeve ought to cover it.
Regards, Marv

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Offline BillTodd

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Re: Coax indicator design
« Reply #48 on: November 12, 2010, 03:28:32 PM »
Bill,

Can I encourage you to provide a few measurements for your design, please?  Just the main shaft and the bronze sleeve ought to cover it.

No problem Marv

The attached drawing are for MkI - I'm sure you can extrapolate to the MkII if you need to :)

The drawings are as designed rather than as made so, for instance,  I made the large diameter of the shaft 19mm (~3/4") because the A4 bolt I used as stock would not quite give me 20mm once surfaced. If it's easier to make the 15mm diameter = 5/8" or the 10mm = 3/8" , it won't make any difference to the function of the device.

The bearing ball I used was 5mm but  3/16" or even 1/4" would do, just adjust the holes to suit.

I machined the indicator holder to be a press fit into the side of the body - might have been better to thread it.

« Last Edit: November 12, 2010, 03:40:13 PM by BillTodd »
Bill

Offline mklotz

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Re: Coax indicator design
« Reply #49 on: November 12, 2010, 04:54:38 PM »
Many thanks, Bill.  I have a broken Chinese clone of a Blake that I'll cannibalize for probe and rocker.  It will be satisfying to turn the junk into a useful tool.
Regards, Marv

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