Dore Westbury Build

This topic has 10 replies, 4 voices, and was last updated 22 February 2012 at 20:04 by Andrew Moyes 1.

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19 February 2012 at 14:55 #85242
Brian
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@brian
I am in the process of building a Mk1 Dore Westbury Milling Machine and need guidance. I have all the castings, materials, components and the detailed build instructions and drawings.

The problem is this; I have arrived at the stage where I need to cut the rack in the Quill using only my ML7 Lathe. I have bored the bearing housing both ends of the Quill and had no problems at all machining all the other components for the machine, but cutting the rack as suggested in the manual is daunting.

Solution; I would like to make contact with anyone who has been through the build process of a Mk1 and carried out this operation, who can guide me through, and past, the potential pitfalls.

If this part of the build is not done correctly the work may grind to a halt, because replacement material is impossible to find.

Any help and or comment would be very welcome.
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19 February 2012 at 14:55 #5968
Brian
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@brian
Help and Guidance needed
19 February 2012 at 16:34 #85251
Andrew Moyes 1
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@andrewmoyes1
I built my Mk1 about 30 years ago and don't remember any difficulty in following the instructions for cutting the rack. Have you got the instruction book that accompanied the set of parts? If not, I can send you the relevant bit.

The method suggested is to clamp the quill to the vertical slide facing the chuck. The teeth are cut using a boring head with a long boring bar holding a home made cutter. As it is a rack, the teeth have straight sides so the cutter is easily made. The cunning bit is that the pitch of the teeth is the same as the Myford leadscrew so (assuming you're using a Myford) when you have cut one tooth, you just move the saddle along by one thread of the leadscrew and cut the next tooth.

Andrew M
19 February 2012 at 18:54 #85261
Tony Pratt 1
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@tonypratt1
I too built my Mk1 about 30 odd years ago and cannot remember any dramas with the rack. I used a Myford vertical slide and I believe all went smoothly, use the shortest and biggest diameter boring bar you can and also use at least 2 clamping bolts to hold the quill in position. Go for the most rigid set up you can and take it slowly.

Tony
21 February 2012 at 10:56 #85373
Brian
Participant
@brian
Andrew/Tony, thanks for the feedback, I have the build instructions and drawings of the rack profile.My main concern is first the grinding of the cutting tool and the depth of cut I should take at each pass. The guidance packing should be placed under the Quill, indicating a full depth cut. Brian
21 February 2012 at 10:57 #85374
Brian
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@brian
I realy should read the text before I post, sorry.
21 February 2012 at 19:58 #85393
Andrew Moyes 1
Participant
@andrewmoyes1
Brian – I remember now – when I machined the rack teeth in the quill, I could not think of a way to reliably depth the teeth to give the right amount of backlash with the pinion shaft. So I fitted an eccentric bush to allow the depth of mesh to be adjusted.

I bored out the hole for the pinion shaft (item 401) in the spindle head (item 312) from 7/8" to 1.1/8" and fitted a cast iron bush with the 7/8" hole bored off centre by 3/32". I was able to eliminate all but the tiniest amount of backlash and locked the bush permanently in that position with a grub screw. Well worth the extra trouble.

Andrew M
21 February 2012 at 19:58 #85394
Andrew Moyes 1
Participant
@andrewmoyes1
Brian – I remember now – when I machined the rack teeth in the quill, I could not think of a way to reliably depth the teeth to give the right amount of backlash with the pinion shaft. So I fitted an eccentric bush to allow the depth of mesh to be adjusted.

I bored out the hole for the pinion shaft (item 401) in the spindle head (item 312) from 7/8" to 1.1/8" and fitted a cast iron bush with the 7/8" hole bored off centre by 3/32". I was able to eliminate all but the tiniest amount of backlash and locked the bush permanently in that position with a grub screw. Well worth the extra trouble.

Andrew M
21 February 2012 at 21:24 #85401
Brian
Participant
@brian
Thanks Andrew,

when you cut the rack, did you follow the suggested method in the book mounting the Quill on a vertical slide? And how did you manage to grind the cutter, with a tool grinder or freehand. It needs to have an inclusive angle of 29 degrees with a tip width of 0.039 inches.

Brian
21 February 2012 at 21:25 #85402
Sub Mandrel
Participant
@submandrel
Hi Brian,

You ask about grinding a tool to cut the rack – all you need to do is grind straight V-edges to the tool at the pressure angle for the gears, as a rack, being a section of a 'gear of infinite diameter' has straight flanks to the teeth.

Neil
22 February 2012 at 20:04 #85484
Andrew Moyes 1
Participant
@andrewmoyes1
Brian – I ground the cutter by hand as I don't have a tool and cutter grinder. On an application like this, the odd degree or so of error can be tolerated. I ground each side in turn using the protractor head of a combination square set to the half angle and held against the shank of the cutter blank. The tip was measured with a micrometer and the end ground off until it was 39 thou as per drawing. Maybe not to the usual engineering tolerance but good enough and it worked perfectly. Go for it!

Andrew M
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