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Difficulty maching mild steel at very small diameters
- Thread starter ChristheClockGuy
- Start date
- Joined
- Dec 20, 2012
- Messages
- 9,422
Chris, I am not a clockmaker but I do use a Sherline lathe and I like it. You are working with really small diameters in some rather hard steels so your tools will matter.
I think the biggest issue might be that you're using brazed carbide. I say might because the tip geometry of a brazed carbide tool generates a lot of cutting forces if left in an unmodified condition. Rather than jumping to conclusions, can you either show us your tools or describe them? What kind of nose radius do they have? Have you changed the original tool geometry at all?
I ask because you're working with tool steels and they can work harden if your tool is not cutting continuously. If the work hardens then it is harder to bring it to precise dimensions and will also make it more likely to snap off if excessive tool pressure is used. Brazed carbide tools will work for you but they typically have fairly shallow relief angles and little, if any, rake. They are also not typically sharp as received. You can modify them with a green silicone carbide wheel or a diamond wheel and they will work better for you, provided you know what you're doing.
A better option would be to use HSS lathe tools or gravers. I say better because HSS tools are easily ground on a bench grinder or belt sander that is more likely available to you. If I had to cut small diameters like you're shooting for, I would use a cobalt HSS knife tool with a 1/64" nose radius, 15 degree relief angles on the side and end, 15 degrees of side rake and about 12-15 degrees of back rake. I would hone it with diamond stones to get rid of grinding marks, then use a fine India stone to hone it well. Finally, I would use a Translucent Arkansas stone to polish it. A tool that is ground and honed like this will cut small diameters readily and will take cuts in the tenths. It is not good for stock reduction though; a general purpose tool would work better for that. So, I would rough it with a general purpose tool and then switch to a knife tool to get it down to size. I would use cutting oil for all cuts.
Gravers will also readily cut your small diameters. In experienced hands, gravers can turn very precisely and will work well for one-off parts.
Your lathe will work for this, Chris. Just use the right tools and you'll do fine.
I think the biggest issue might be that you're using brazed carbide. I say might because the tip geometry of a brazed carbide tool generates a lot of cutting forces if left in an unmodified condition. Rather than jumping to conclusions, can you either show us your tools or describe them? What kind of nose radius do they have? Have you changed the original tool geometry at all?
I ask because you're working with tool steels and they can work harden if your tool is not cutting continuously. If the work hardens then it is harder to bring it to precise dimensions and will also make it more likely to snap off if excessive tool pressure is used. Brazed carbide tools will work for you but they typically have fairly shallow relief angles and little, if any, rake. They are also not typically sharp as received. You can modify them with a green silicone carbide wheel or a diamond wheel and they will work better for you, provided you know what you're doing.
A better option would be to use HSS lathe tools or gravers. I say better because HSS tools are easily ground on a bench grinder or belt sander that is more likely available to you. If I had to cut small diameters like you're shooting for, I would use a cobalt HSS knife tool with a 1/64" nose radius, 15 degree relief angles on the side and end, 15 degrees of side rake and about 12-15 degrees of back rake. I would hone it with diamond stones to get rid of grinding marks, then use a fine India stone to hone it well. Finally, I would use a Translucent Arkansas stone to polish it. A tool that is ground and honed like this will cut small diameters readily and will take cuts in the tenths. It is not good for stock reduction though; a general purpose tool would work better for that. So, I would rough it with a general purpose tool and then switch to a knife tool to get it down to size. I would use cutting oil for all cuts.
Gravers will also readily cut your small diameters. In experienced hands, gravers can turn very precisely and will work well for one-off parts.
Your lathe will work for this, Chris. Just use the right tools and you'll do fine.
Last edited:
- Joined
- Oct 9, 2019
- Messages
- 9
Thanks Mikey and all posters for your replys. I am using quality Micro-100 D4 and AR-4. unmodified. These particular cutters come recommened and do the job. I am currently investigating resetting the cutter height as it could be just a tad off centre pushing the tiny diameter rather than cutting. Any advice on how to sharpen these brazed carbide tools appreciated.
Chris
- Joined
- Nov 21, 2015
- Messages
- 56
Hi Chris, you're in the same area as myself...
I've sharpened brazed carbide tools on a bench grinder with a CBN wheel (probably not best for the wheel) and also with a diamond wheel - the sort with a diamond matrix in a binder on the edge of a cup wheel. The latter one isn't too expensive. I also made sure to relieve the steel of the holder on a normal grinding wheel first so the diamond didn't have to do too much work. I got my diamond wheel from RDG Tools, less than £20, so not too pricey. I have a T&C grinder to set the angles when it really matters, eg for threading tools.
Please PM me if I can be of any help.
Rob
I've sharpened brazed carbide tools on a bench grinder with a CBN wheel (probably not best for the wheel) and also with a diamond wheel - the sort with a diamond matrix in a binder on the edge of a cup wheel. The latter one isn't too expensive. I also made sure to relieve the steel of the holder on a normal grinding wheel first so the diamond didn't have to do too much work. I got my diamond wheel from RDG Tools, less than £20, so not too pricey. I have a T&C grinder to set the angles when it really matters, eg for threading tools.
Please PM me if I can be of any help.
Rob
- Joined
- Dec 20, 2012
- Messages
- 9,422
At the diameters that you're working with those tools are apparently not doing the job, and I suspect the reason is deflection. I'm all for Micro 100 tools and I have used and like their brazed carbide tools but on tiny diameters they will deflect far more than a properly ground HSS tool will and that's a fact.
The impact of this deflection is that you will not be able to get the tool to cut at the depth you dial in due to excessive cutting forces. Since the tool itself is rigidly mounted and cannot deflect, those cutting forces will cause the work piece to deflect both down and away from the cutter and you will have inaccurate diameters and broken work pieces. This can occur even if the tool tip is mounted at center height because it has to do with the tip geometry more than anything else.
Since you seem to be convinced that carbide tools are the way to go then I suggest you use a diamond wheel to sharpen them. Put at least 10 degrees of relief angle on the side and end and see if you can grind at least some side and back rake into the insert. Keep the nose radius as small as you can but do put a radius on there. Hone it to as fine an edge as you can with an extra-fine stone and then see how it goes.
If you're going to work with tiny diameters a lot, I highly recommend you learn to grind HSS tools at some point.
- Joined
- Nov 27, 2012
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- 7,912
I don't know the holder designation off the top of my head for that particular insert orientation but those style holders are old, or should I say have been around for a long time. They use TP/TPG inserts. The inserts don't have a hole for mounting, they're just clamped in place. Search TPG holder & you should be able to find it. TP inserts have been around for a long time so good thing is you can find them for really cheap.
- Joined
- Nov 17, 2017
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- 1,525
I grind my carbide tools with the same stones I use to sharpen my exacto blades.
- Joined
- Dec 26, 2017
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- 60
By chance have you ever watched Clickspring's (aka Chris) videos on YouTube. His and Pieczynski's videos are full of tricks and tips.
Clockmaking looks challenging but if it's not a job I think it would be fun
And it allows you to be really creative.For what it's worth... Grinding HSS tools is far easier than it looks.