Author Topic: Putting graduations on dials - a simple depth stop.  (Read 3429 times)

Offline andyf

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Putting graduations on dials - a simple depth stop.
« on: April 15, 2010, 01:21:06 PM »
I needed to re-engrave the topslide dial collar on my lathe. Some Chinese person had fitted the wrong one, showing 50 thou per turn when it should have shown 40  :hammer: . Because I don’t use the topslide dial for measuring, even when threading with the slide set over at an angle, it’s taken 4 years to realise something was wrong. But you know how it is – once noticed, things like this nag at you :poke: until you do something about them. 

I liked the look of Mike Burdick’s method (of scribing the marks, not stamping numbers) at
 http://www.neme-s.org/images/PDF_Files/Making_Graduated_Collars1.pdf  .
He uses a long boring bar type tool, plunging in and pulling it out from the inner end of the mark, rather than pushing in from the edge of the dial.

It struck me that there was an easier way to get the graduations to the right length than his method of measuring each one individually using his handwheel dials.  Here’s my rough and ready tool, holding an HSS V bit; no point cutting off the excess, because the full length might come in useful sometime. The USP is the threaded section with a washer secured between two nuts.



With the dial collar on a mandrel, the existing markings were turned off. Forty new graduations were needed, with every 5th and 10th being longer than the rest. O joy unbounded - 40 marks, and 40 teeth on my spindle gear  :)
An improvised detent was made by bolting a changewheel immoveably to the top of the banjo, so it could be swung in and out of mesh with the spindle gear to do the indexing. The dial collar was blacked up to make the marks more visible. The next pic shows the short “unit” markings being applied using the washer as a depth stop against the fat washer holding the work on the mandrel – as can be seen, the fat washer is actually an old gearwheel which just happened to be the right bore and diameter. Then, it was just a matter of winding the carriage handwheel until the depth stop hit, plunging in with the cross-slide (using its dial for uniform depth of cut), dragging the tool to the right with the carriage handwheel, withdrawing the cross-slide, indexing round a notch and repeating. 



I engraved 32 short marks in sets of four with a gap between each set, then reset the depth stop and put in 8 longer ones for the 5s and 10s. Here’s the result.



It needs numbers (0, 10, 20 and 30) punching in, which I’ll do on the mandrel to avoid distorting the collar or leaving bumps on its inner surface. Mike Burdick’s method of whacking numbers into work held in the chuck doesn’t sound as if it would do the spindle bearings and chuck much good. A jig will be needed to try and get the numbers looking nice, but even with a jig I find it hard to get professional looking results, particularly on a 1½” diameter curved surface, so the finished dial probably won’t be photogenic.

Andy


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

Offline Bernd

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Re: Putting graduations on dials - a simple depth stop.
« Reply #1 on: April 15, 2010, 06:22:17 PM »
Nice solution to depth control. I like it. Very good.  :thumbup:

Bernd
You can't fix "STUPID".

Offline Brass_Machine

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Re: Putting graduations on dials - a simple depth stop.
« Reply #2 on: April 15, 2010, 09:00:18 PM »
Nice job with that Andy!

Another good one to file away!

Eric
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Offline CrewCab

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Re: Putting graduations on dials - a simple depth stop.
« Reply #3 on: April 16, 2010, 04:57:03 PM »
Nice going Andy  :thumbup:

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