MEW 178 – Unimat 3 Tailtock Capstan

[Gray62Participant @gray62]

I read the above article with interest, and with a view to adapting it to my Warco GH1330.

The part that really interested me was the method to produce the rack as I have another application awaiting a rack.

Then I read this and got all confused:

 

‘A section of 12mm roofing bolt will produce 2 racks…etc

Clamp the bolt lengthwise…’

And this is the confusing bit

‘remove one side of the bolt to a point 3mm above its diameter’

 

Am I misreading/misunderstanding this or is this a misprint.

 

Help before I go completely mad, I have read this several times and it still does not make sense to me

 

cheers

 

Graeme

[Gray62Participant @gray62]

Is my brain finally giving up on me ?

[David Clark 13Participant @davidclark13]

Hi There

Measure from the outside diameter of the thread to the inside face that has been cut away. Simples.

regards david

 

[Geoff SheppardParticipant @geoffsheppard46476]

I think that the writer is trying to instruct the builder to machine most of one side of the roofing bolt down to a point 3mm above an imaginary diametral line. By then turning the bolt over and clamping the newly machined face down to the machine table, the other side can be machined down to leave a total thickness of 6mm. This results in 3mm being left on “the other side” of the diametral line, so that the 6mm is disposed equally about a this line.

 

What I am now trying to work out is how to measure the position of the first machined face if the bolt is dropped into a tee slot (good practice in my view) instead of being placed on to the surface of the table. I suppose the trick is to measure the diameter over the bolt threads before putting it in the tee slot, then to measure the distance between the top of the threads and the table surface when it is in position. This allows the height of the diametral line to be calculated. Add 3mm and the height of the required machined surface is established.

 

Sounds a bit complicated, but hope it helps.

[JasonBModerator @jasonb]

Touch the cutter on the crest of the threads and make a not eof the quill reading or zero the Z-axis DRO and then keep feeding down for 3mm (assuming teh OD is 12mm)

[Geoff SheppardParticipant @geoffsheppard46476]

Probably close enough, but could be a bit under-size. Checking a piece of studding at random, it measured 11.81mm.

[Jeff DaymanParticipant @jeffdayman43397]

I think what is being instructed is how to make a rack out of a commercial bolt.

 

1. This will produce a “rack” with curved face helically cut teeth. It will not engage a spur pinion properly and will transmit very little torque, both of which a proper cut rack would. If a “pinion” follower were made like a lathe half nut this would engage such a “rack” far better than a spur or helical pinion.

 

2. Surface finish of a commercial bolt may not be good, and there may be signifiicant errors of several types in the thread.

 

Even for home shop use this idea sounds like a bad bodge, and not a good idea. If it were me, I’d buy a miniature rack and pinion from one of the commercial gear houses. Davall do them in UK, Stock Drive Products do in USA.

 

Davall’s website is at http://www.davall.co.uk/stocksales.php

 

Stock Drive Products is at http://www.sdp-si.com/

 

Do it once and do it properly.

 

JD

[JasonBModerator @jasonb]

Posted by Geoff Sheppard on 06/06/2011 21:49:36:

Probably close enough, but could be a bit under-size. Checking a piece of studding at random, it measured 11.81mm.

 

In that case just feed down 2.905mm

 

11.81 – 6 = 5.81 div 2 to take the same off each side = 2.905mm

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