rack cutting

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rack cutting

This topic has 5 replies, 4 voices, and was last updated 24 February 2016 at 19:33 by Simon Williams 3.

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24 February 2016 at 17:16 #226738
Tractor man
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@tractorman
Hello all. I need to cut a rack on my model pillar drill quill sleeve. I have found a suitable pinion gear. What do I need to know about the pinion gear to get the right cutter. Would making a form tool for the shaper be a better way that using a gear cutter in the mill? Never attempted any gear cutting at all so any advice or reference material gratefully received. Mick
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24 February 2016 at 17:16 #24400
Tractor man
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@tractorman
24 February 2016 at 17:22 #226740
Michael Gilligan
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@michaelgilligan61133
Posted by Tractor man on 24/02/2016 17:16:54:
Hello all. I need to cut a rack on my model pillar drill quill sleeve. …

Would making a form tool for the shaper be a better way that using a gear cutter in the mill?

.

Just as good, and a heck of a lot cheaper.

MichaelG.
24 February 2016 at 19:03 #226751
Fatgadgi
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@fatgadgi
Hi Mick

You need to know the Module (or DP) of the gear and the Pressure Angle. That's all.

Involute cutters are sold to cut (to a reasonable approximation) within a range of teeth, but the rack cutters (they have "rack" written on them) are dead simple, just straight sides to the tooth. You can easily work it out from standard formulae, for example:

http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf

But Michael's right, making a cutter is easily possible and probably quite a bit cheaper, especially for a one-off. But of course, suitable material is also costly and the accuracy will probably be less than a bought one. And you can normally pick them up second hand if you are lucky for between £10 and £20

Cheers – Will
24 February 2016 at 19:12 #226752
Fatgadgi
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@fatgadgi
Hi Again Mick

As well as using the shaper to plane the teeth, which could be a bit harsh if the rack is delicate, involute or fly cutters can also be held between centres in the lathe and the rack held on the cross slide perhaps ?

Cheers – Will
24 February 2016 at 19:33 #226756
Simon Williams 3
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@simonwilliams3
Good evening Mick, I've been mulling over the way to solve exactly the same problem (and for the same application!) for some time now. It seems to me that the problem with cutting a rack in a milling machine – either horizontal or vertical – is running out of travel. If you mount the cutter on an arbour in a horizontal mill you've only got the travel of the y axis before you run out of space to index to the next tooth. So you really want to mount the work at right angles to the table, and also turn the axis of the cutter through 90 degrees. Keith Fenner has got a suitable gadget on his K&T mill, but I don't aspire to anything as fancy.

I could also cut the rack with the cutter in the vertical mill, but now the length of the rack I can cut is constrained by how much overhang of the cutter off the quill is bearable. Not much!

Fair play to Will, I hadn't thought of using the length of the lathe bed as the axis of the length of the rack. I don't have a DRO but if I could fettle up something with a long vernier caliper to measure the incremental position of the saddle under the cutter I'd be in business. Not sure I trust the leadscrew to do this measurement, but I guess that depends on the age of the lathe. Anyway. I happen to have a piece of precision ground 1" dia steel to use as an arbour. Just pop a key way in it and a couple of threads for locknuts and I'll give it a try.

Rgds

Simon
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