relieving attachment

I have seen a few videos on youtube of relieving attachments in use for cutting gear hobbers. Some lathes come with a relieving attachment. Can anyone describe in a few well chosen sentences what the relieving attachment does and other uses ?.

I think it moves the cutting tool in and out, you gear it to the spindle so it moves to suit the number of teeth per rev. This would be for a 4 tooth cutter, the red outer path is shown on the right and what it looks like with the teeth cut on the left so you get clearance behind each tooth

If I think very hard I can sort of see what you mean , very nice diagrams , but how do you wind the cut in ?. It must ? come back to the same starting point.

I went around SYKES gear cutting works a long time ago and I remember the relieving lathes made one hell of a din. There was as much lubricating oil used on the relieving cam as coolant for the piece being cut. Looked impressive as the workpiece (a gear hob) was revolving at about 500 Rpm. I would have thought it outside the scope of ME's - but then there is always someone who goes where others fear to tread.

BobH

You can get the general idea of how it's done here by offsetting the work. A relieving attachment does the same thing automatically and indexes round to each point required on the tool. Sometimes 1 point on one rev and another on the next.

**LINK**

There is also a better way of putting a gear cutter form on them than shown here. It uses the top of 2 round button set a certain distance apart and at an angle.

There was model engineer design for an attachment and also details of the form tool for gears. You might find details of both on the web.

John

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Cut is put on with the cross slide and toolholder/post moves about due to the cam in its base

Couple of examples here show various setups

I'm pretty sure the Model Engineer one moved the work. Usually made of mild steel so they can jam up and need lots of grease - just in case some one is tempted. Might be better to use cast iron.

John

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Eureka attachment, details are in Gears and Gearcutting, Ivan Law, Workshop Practice Series, No.17.

Daveb

**LINK**

Demonstrates how the Eureka works.

Rod

For commercial gear hobs and involute cutters the operation needs to be a bit more subtle than just ensuring relief of the cutting edge. The correct form also needs to be maintained, so that when the cutting face is sharpened on a radial the cutter gets a bit smaller in diameter, but exactly the same tooth form is maintained.

Andrew

It does cut the form as well Andrew so that they can be ground back. Not much point using one otherwise.

John

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Giles Parkes built one to fit on a Myford and he was demonstrating it at one of the shows on a show donated lathe from Myford but they made him stop as they were frightened it was overloading the lathe.

Without looking a dare say it is in one of the MEW's.

Plenty of old time toolroom lathes had these as attachments. Go to lathes.co.uk site and look up Hendy for a start.

You do need a decent solid lathe though because of the loadings involved.

It pre dates MEW. I believe it was in Model Engineer. Personally I feel that the method I linked to is an easier option and 4 points is a lot better than a fly cutter with a form on the end of it.

One thing about Eureka is that it's not that easy to see how it works from the detail I saw in a mag some time ago. The video helps a lot.

So Myfords shouldn't be used for interrupted cuts. I know they have limitations but didn't think it was that bad.

John

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It's not just Myford, it's any light lathe.

Imagine it, you have a lathe doing say 80 revs and it relieving a hob with 12 gashes. That's 960 times per minute it has to hammer the slide in against a quite aggressive cam.

The form cutter relieving device I saw in a toolroom some years ago used change wheels as in screw cutting but driving an additional articulated shaft connected to a topslide which was cam driven to cut and returned by a very strong spring. Due to the large surface contact with the cutter being relieved ("backed off" a lot of cutting force is involved and the lathe needs to run very slowly for this reason and to get a good surface finish. I think that the lathe I saw was a 6 inch centre height Hendy. Colin

I'm a Boxford owner John so may be inclined to jokingly pass comments about Myford. Some do. I have owned a Myford too. it started as an ML7 and later turned into a Super 7. Sold before it was fully sorted out because the Boxford came up with a lot of tooling.

Personally I would be more worried about the effects on the head stock bearings than the slides due to the number of times the cut starts. The relief has to be generated slowly, not in one go. I run my slides fairly tightly anyway which would help. I do this for finish and very light cuts when needed. I'm a finish fanatic I'm afraid.

John

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I made a Eureka many years ago and used it on my Boxford to form relieve a gear hob I was making. It worked absolutely fine, though I did use a low speed.