Parting Off a Piece with multiple holes in the centre

[Aidan BrowneParticipant @aidanbrowne70238]

Hi,

 

I'm making a pair of eccentic chain tensioners for a project I'm working on. The piece is a 38mm stainless steel bar. I have drilled a 12mm hole for the axle and 2 x 8mm holes for the tensioning tool to tighten the axle.These are like a trangle inside the diametre of the piece. I have a small clarke lathe. I tried parting off and the moment the parting tool (It's a glanza tool with inserts and a 2mm wide tip), broke through the first hole it jamed and bent the tool holder and the tip fell out. Before that it was curling off swarf perfect. I reversed the tool in the holder and fed it in at a slower rate and near the centre I heard a crack and the tip of the tool broke. I've no formal training on the lathe and any help to point out where I'm going wrong would be really appreciated. 

Image of something similiar if it helps

http://www.webbikeworld.com/motorcycle-maintenance/chain-adjustment/pinch-bolt.jpg

 

Thanks,

Aidan.

Edited By Aidan Browne on 04/06/2012 00:25:28

Edited By Aidan Browne on 04/06/2012 00:26:07

Edited By Aidan Browne on 04/06/2012 00:27:57

[Aidan BrowneParticipant @aidanbrowne70238]

Parting of an eccentic chain tensioner

[Ady1Participant @ady1]

The tool tip is under pressure… everythings going great with a steady stream of swarf…

tool breaks into first hole and pushes forwards, tool tip now cutting 2x 3x 4x the amount it was a millisecond ago, and bang

an ultra slow feed rate might help, but it would probably blunt the tool

Doing anything you can to maximise stiffness would reduce the amount the tool "springs" forwards when it breaks through

If you can't improve stiffness then an upside down tool at the back will have more chance of survival than a tool at the front

[Ady1Participant @ady1]

Parting off seems to be a bit of a black art on smaller machines because they are not so rigid

Big machines with lots of stiffness and power make it look like a doddle

On my own machine I found a rear parting tool and backgear engaged (50rpm- lots of torque) with a slow feed rate gave me the best chance of success

Higher speed stuff was a bit of a lottery with lots of failures

[Jeff DaymanParticipant @jeffdayman43397]

Thought 1 – take the work out of the lathe, saw it on a bandsaw, return it to lathe to face the end to size. This is by far the safest and easiest way, and there's no shame in sawing when parting is not working out.

Thought 2 – make close fitting bungs of the same metal, loctite into the holes (to make a workpiece as solid as possible, no holes in the area to be parted), part off, heat the work to release the loctite, pull out the bungs. The bungs could be made a little long to help the pullout, or made with short threaded holes to jack them out.

JD

[John CoatesParticipant @johncoates48577]

Out of interest Aidan what motorcycle is the adjuster from? Looks similar to the single sided swingarm on a VFR

John

[DustyParticipant @dusty]

I would go with Geoff's first option. You would have problems even with a rigid lathe. I have, over the years, done a lot of parting off and I would not entertain doing it on a small lathe. You would need to return it to the lathe anyway to face it, as the finish is going to be rougher than a Bears ar**e. No need to make things anymore difficult than they are.

[Engine BuilderParticipant @enginebuilder]

You could plug the holes with a rod of the same material superglued in place, then it would be just like parting a solid bar. A little heat will allow the bars to be pushed out afterwards.

[KWILParticipant @kwil]

Out of interest, why not start with a blank disc, faced both sides and then put the 12 and 8mm holes in?

[Ian S CParticipant @iansc]

I would not try to part off a bit like that (particulary stainless),This needs to be kept cutting, too fine a cut and it rubs, and hardens. You could part it to just short of the holes, the cut off with the hacksaw/bandsaw. Ian S C

[Aidan BrowneParticipant @aidanbrowne70238]

Thanks for everyones time to give me advice.

I drilled the holes in the piece first as I put it in the Mill and it saved me changing chucks and spending time messing with the 4 jaw trying to set it up plus with my measuring I'd probably be out between the 2 pieces. I was hoping to part it off because the amount of stock I have is fairly tight.

I think the best suggestion on the board is to take it out and cut it witht the band saw and face it. I think because it's 19mm to the centre my parting off tool is out further than I've ever had it out before and is vibrating a lot.

By the way it's for a custom swinging arm I'm making for cub90. Bit off the wall but it keeps me out of the pub. **LINK**

I'll let you know how I get on.

Thanks.

[John CoatesParticipant @johncoates48577]

Ooh Aidan I love stuff like this. I'm putting a ZX14 complete front end on my ZX7r which needs the steering stem adapting and a ZX10R swingarm which needs spacers.

In the last picture on your link it shows the two adjusters seemingly parted off so did you get it sorted?

John

[Aidan BrowneParticipant @aidanbrowne70238]

Got sorted anyway. I took the advice above and cut them with a stainless cutting disk in the small grinder then faced them. Worked out nicely, just had 2mm of extra stock when finished.

Hi John, that's some pretty heavy duty modification your doing. You'll have some severe stopping power when you make those modifications. Send me a pic when your done.

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