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How to machine Acetal

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Mick B116/06/2019 19:22:56
1069 forum posts
59 photos

Smart work. laugh

Presumably it's not just rake you'd need when cutting, but a helluva lotta trailing side clearance to avoid rubbing on the helix angle.

I meant to ask: would have been easier to find a way to re-use the business end of the existing stirrer by joining to a new stem in some way?

 

Edited By Mick B1 on 16/06/2019 19:25:44

Ian Johnson 116/06/2019 21:58:42
59 forum posts
15 photos
Posted by AdrianR on 16/06/2019 10:18:40:

Well it turned out OK in the end, I made a couple of mistakes which ruined the finish in places, but I am happy with it.

I rounded the part that broke and the camera angle makes it look a lot longer,

dscf0961.jpg

That turned out nice. Looks like a very aggressive square thread! And there is always more than one way to get the job done.

I tend to use tips with a good positive top rake for all my general machining these days, and apart from form tools I try to avoid grinding HSS, it's just too messy!!!. My favourite tips are these DCMT 070204 with the ground/polished finish, they will machine anything, brass, aluminium, steel etc. and are very good on plastic especially Acetal.

Ian

Carbide tips

Martin Hamilton 116/06/2019 22:24:47
97 forum posts
Posted by Ian Johnson 1 on 16/06/2019 21:58:42:
Posted by AdrianR on 16/06/2019 10:18:40:

Well it turned out OK in the end, I made a couple of mistakes which ruined the finish in places, but I am happy with it.

I rounded the part that broke and the camera angle makes it look a lot longer,

dscf0961.jpg

That turned out nice. Looks like a very aggressive square thread! And there is always more than one way to get the job done.

I tend to use tips with a good positive top rake for all my general machining these days, and apart from form tools I try to avoid grinding HSS, it's just too messy!!!. My favourite tips are these DCMT 070204 with the ground/polished finish, they will machine anything, brass, aluminium, steel etc. and are very good on plastic especially Acetal.

Ian

Carbide tips

Ian where did you get those particular dcmt inserts from if you dont mind me asking, thank you.

Ian Johnson 117/06/2019 00:41:14
59 forum posts
15 photos

Hi Martin I get those tips from JB Cutting Tools. They usually have a stall or two at classic bike shows (Stafford), steam fairs or model engineering shows. I think you can order on-line too although I haven't tried that yet. I don't know the technical specification for the tips, but if you ask Jenny she will give you the same ones, very good quality. About £3.50 each Silver or Gold I think they are the same spec, gold is prettier though!

Ian

Daniel17/06/2019 07:16:33
avatar
205 forum posts
37 photos
Posted by Ian Johnson 1 on 17/06/2019 00:41:14:

Hi Martin I get those tips from JB Cutting Tools. They usually have a stall or two at classic bike shows (Stafford), steam fairs or model engineering shows. I think you can order on-line too although I haven't tried that yet. I don't know the technical specification for the tips, but if you ask Jenny she will give you the same ones, very good quality. About £3.50 each Silver or Gold I think they are the same spec, gold is prettier though!

Ian

I order regularly through their online shop.

Their website is great to navigate and the whole process very simple.

ATB,

Daniel

AdrianR17/06/2019 08:58:00
226 forum posts
19 photos

Smart work. laugh

Presumably it's not just rake you'd need when cutting, but a helluva lotta trailing side clearance to avoid rubbing on the helix angle.

I meant to ask: would have been easier to find a way to re-use the business end of the existing stirrer by joining to a new stem in some way?

I must admit I did not worry about clearance, The tool was quite small and had a good front clearance so it did not interfere much.

I did think about fixing the old one but;

  • The plastic feels like the type that doesn't glue well.
  • I thought of splinting with a stud down the middle, and in fact the motor spindle end is threaded, but the motor runs backwards and it would unscrew.
  • I thought of making a socketed sleeve, but I am not sure how good the alignment between the motor and the oil tube is, so It could end up stressing the shaft.
  • The mill is 19 years old, and the plastic could be brittle.
  • There is no way to know if the oil pump is working.

So I decided making a new one is probably the safest. The Acetal does seem to be slightly more flexible than the old one, and I have strengthened the point that broke.

Adrian

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