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Cutter Advice for silver steel Micro machining

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Chris TickTock02/11/2019 09:34:10
591 forum posts
41 photos

staff showing undercut.jpgHi, I have been learning to use my Sherline lathe whilst simultaneously attempting to make a balance staff for a platform escapement off a clock. I have now largely succeeded as you can see from the photo of the first one i made from mild steel for practice. I have been using quality brazed carbide cutters upon recommendation and founfd this advice largely holds as the cutters have held their edge and no chips can be seen.

So why the post well if you look at the photo one of the things it is necessary to produce is an undercut shown with the arrow. Baring in mind the cutter has to enter the shoulder without reducing the shoulder length on A you can understand with only a few thou this is delicate work. I would add I do this machining under optics otherwise not possible. Various questions arise as to possible improvements to cutters used as follows;

1. The cutters I have used are termed super carbide as they resist chipping and hold their edge, they come pre-sharpened. However they are U.S products (Micro-100) do we make anything equivalent?

2. Posters have argued that aluminium inserts could be used to machine silver steel that being the case I have been wondering if the 35 degree aluminium rhombus in a suitable holder would be suitable for machining the undercut having a sharp angle. I realise that sharper angles wear more quickly just wondered if only used for this small usage whether it is suitable. If it is can anyone suggest a holder for the V shape rhombus for something usable on the Sherline. The Sherline comes with 1/4 inch tool posts but there are 5/16 and 3/8 posts which I also have.

Regards

Chrisstaff showing undercut.jpg

David George 102/11/2019 10:09:36
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1339 forum posts
448 photos

Have you considered using HSS and grinding your own tools as I have no problem turning silver steel with quality tool bits especialy when you need a special form or shape. I use HSS for most of my general turning finishing.

David

Bob Stevenson02/11/2019 10:10:42
436 forum posts
7 photos

Personally I would never attempt to make horological undercuts like that...ie, with the cutter 'diamond' approaching along the centre line of the work. I usually do this job with HSS bit that I have ground specially, and use at 90 degrees to centre line while keeping true on the dimension of 'A' in your pic....this is actually a very simple end task which takes only moments (to cut the undercuts)

 

I do mainly use carbide replacement tools for nearly all turning in both brass and steels but always use HSS bits for undercuts, grooves and seatings etc....for undercuts grind a square ended tool and then grind a slight side angle for the undercut...just run the tool up to the shoulder and let the angle 'whisper cut' the undercut.

 

Hope this helps!

 

EDIT;  I was working on my post when David posted and I see that he concurs with what I posted...He is (judging by his posts) a very experienced machinist so you can consider our posts as complimentary!

Edited By Bob Stevenson on 02/11/2019 10:20:37

John Haine02/11/2019 10:30:40
3338 forum posts
178 photos

Tangential ("Diamond" tool - here is a description of one I made for the Unimat.

**LINK**

img_1344.jpg

And I made a small version of the Turnado which takes the same holder, useful maybe for horology.

**LINK**

img_20181216_170520235_hdr.jpg

Uses 3/16 HSS tool blanks, cheap and easy to sharpen.

Edited By John Haine on 02/11/2019 10:32:21

roy entwistle02/11/2019 11:00:16
1252 forum posts

Fairly easy with graver by hand

Roy

Chris TickTock02/11/2019 11:17:11
591 forum posts
41 photos
Posted by Bob Stevenson on 02/11/2019 10:10:42:

Personally I would never attempt to make horological undercuts like that...ie, with the cutter 'diamond' approaching along the centre line of the work. I usually do this job with HSS bit that I have ground specially, and use at 90 degrees to centre line while keeping true on the dimension of 'A' in your pic....this is actually a very simple end task which takes only moments (to cut the undercuts)

I do mainly use carbide replacement tools for nearly all turning in both brass and steels but always use HSS bits for undercuts, grooves and seatings etc....for undercuts grind a square ended tool and then grind a slight side angle for the undercut...just run the tool up to the shoulder and let the angle 'whisper cut' the undercut.

Hope this helps!

EDIT; I was working on my post when David posted and I see that he concurs with what I posted...He is (judging by his posts) a very experienced machinist so you can consider our posts as complimentary!

Edited By Bob Stevenson on 02/11/2019 10:20:37

Thanks Bob any chance of you showing sketch or photo as still unsure exactly what you mean.

regards

Chris

Martin Connelly02/11/2019 19:20:11
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1463 forum posts
168 photos

Chris, reading your original post I get the impression that you think aluminium inserts are made of aluminium. This may not be the case but if it is I would like to point out that these aluminium inserts are carbide ones designed and made to cut aluminium. They will not wear any more quickly than other carbide inserts.

Martin C

Chris TickTock02/11/2019 22:33:22
591 forum posts
41 photos
Posted by Martin Connelly on 02/11/2019 19:20:11:

Chris, reading your original post I get the impression that you think aluminium inserts are made of aluminium. This may not be the case but if it is I would like to point out that these aluminium inserts are carbide ones designed and made to cut aluminium. They will not wear any more quickly than other carbide inserts.

Martin C

Thanks Martin, the truth is I did not know what they were made of but knew they were sharp and were designed tocut aluminium, so thanks for the clarity. Unless I have missed some one saying so no one has commented on whether the rhonbus 35 degree could successfully be used to undercut Silver Steel.

Chris

Chris

John Haine03/11/2019 07:21:07
3338 forum posts
178 photos

Only one way to find out, why don't you try it?

JasonB03/11/2019 07:37:18
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Posted by Chris TickTock on 02/11/2019 22:33:22:. Unless I have missed some one saying so no one has commented on whether the rhonbus 35 degree could successfully be used to undercut Silver Steel.

Chris

Without knowing the angle of the undercut it is impossible to say. Given the very small diameter of the work I would be worried about the bottom edge of the insert rubbing.

JasonB03/11/2019 07:57:01
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Forget using an insert, the most pointed you will be able to get will have a 0.2mm tip radius so not a chance in hell of that being able to undercut 0.006"

micro muckup.jpg

Even if you went for a Warner ground HSS insert which may have a bit more of a point the edge would rub.

So do as suggested grind a special, use a hand graver or ask your expert.

Chris TickTock03/11/2019 15:30:12
591 forum posts
41 photos

Thanks Jason, Your drawing demonstrates how difficult it is to machine such an undercut. However having now pursued both advocats of the traditional jewelers lathe verses the machinist route I now have a pretty good basis to air an opinion.

Firstly if using a jewelers lathe then you would need a graver or suitable cutter fashioned to a very fine point held against the shoulder and with light pressure so as not to break its tip an undercut could be made without damaging adjacent material.

Secondly using a lathe such as the Sherline you would have to either use a hand tool rest which there is one for the Sherline or possibly fashion a special tool / tool holder capable of holding such a thin cutter.

Finally it has been suggested to me that possibly the undercut whose purpose is to aid metal to be rivetted to fix the balance wheel on is not critical...this is a contentious point but that is the debate, as yet beyond my grade.

Chris

Neil Wyatt03/11/2019 15:37:17
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This is clearly a job ideal suited to a hand ground HSS tool, which will do the job with no drama.

Neil

Chris TickTock03/11/2019 15:58:16
591 forum posts
41 photos
Posted by Neil Wyatt on 03/11/2019 15:37:17:

This is clearly a job ideal suited to a hand ground HSS tool, which will do the job with no drama.

Neil

Using HSS would be the way to go if it can be ground to a very fine point...can it and remember the cutter will have to be held almost parralel to the sholder so as not to touch where it should not. I have seen a hand graver formed from a tungsten drill held in a pin vice used on a jewelers lathe. if a tool holder could hold a correctly fashioned hss then totally possible on the Sherline. It all comes down to can HSS be ground to such a fine point??

Chris

SillyOldDuffer03/11/2019 16:26:04
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6329 forum posts
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Posted by Chris TickTock on 03/11/2019 15:58:16:
Posted by Neil Wyatt on 03/11/2019 15:37:17:

This is clearly a job ideal suited to a hand ground HSS tool, which will do the job with no drama.

Neil

It all comes down to can HSS be ground to such a fine point??

Chris

HSS can certainly be ground fine - it's one of it's advantages. The limit is usually the chap doing the grinding! Takes a steady hand, practice, and patient work with a fine wheel and/or emery paper. Ideally the point geometry would be the same as a larger cutting tool, just smaller.

Dave

JasonB03/11/2019 16:35:58
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Chris, what is the angle of the undercut, if only a few degrees then easy enough to grind something, if 45deg or more then tool rubbing will be a problem and need allowing for.

You don't need to rush out and buy a special hand rest, a bit of round bar in your toolpost will do fine for starters. I've just been doing a cylinder cover in cast iron that needed concave and convex shapes and just used the shank of a boring bar in the toolpost as a rest and a couple of woodworking HSS scrapers as gravers.

Chris TickTock03/11/2019 17:08:05
591 forum posts
41 photos
Posted by JasonB on 03/11/2019 16:35:58:

Chris, what is the angle of the undercut, if only a few degrees then easy enough to grind something, if 45deg or more then tool rubbing will be a problem and need allowing for.

You don't need to rush out and buy a special hand rest, a bit of round bar in your toolpost will do fine for starters. I've just been doing a cylinder cover in cast iron that needed concave and convex shapes and just used the shank of a boring bar in the toolpost as a rest and a couple of woodworking HSS scrapers as gravers.

Thanks Jason,

To clarify the undercut is best explained by a photo. The idea of the undercut is to leave the top part of the shoulder with thinner metal that can be staked so using it as a rivet to hold the balance wheel on. I thank you for your idea of using a piece of round bar in my tool post as a rest...really simple cool idea.

Another idea I have modified is to gring a 3mm tungsten drill into a cutter and mount this in a 1/4 square mild steel bar with grub screw held in my tool post. if I can get a suitable approach angle this will do the job.

Chrisundercut.jpg

JasonB03/11/2019 17:31:06
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Yes it's that angle that you need to watch.

This is the same insert that I drew above but going to a point, these generally have a 7degree angle which would rib, assumed a 45degree undercut of the part

7deg edge.jpg

Increase that angle and it will fit ok, I went with 27deg

27deg.jpg

Chris TickTock03/11/2019 20:39:52
591 forum posts
41 photos
Posted by JasonB on 03/11/2019 17:31:06:

Yes it's that angle that you need to watch.

This is the same insert that I drew above but going to a point, these generally have a 7degree angle which would rib, assumed a 45degree undercut of the part

7deg edge.jpg

Increase that angle and it will fit ok, I went with 27deg

27deg.jpg

Really appreciate your contribution Jason, thanks

Chris

roy entwistle03/11/2019 21:13:40
1252 forum posts

These have been made by watchmakers using hand held gravers for more years than I care to think about. Many driven by a bow.

Roy

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