Author Topic: Milling threads on the lathe  (Read 5371 times)

Offline Florian Eberhard

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Milling threads on the lathe
« on: November 14, 2013, 05:56:53 PM »
Hi Fellows

Well - as the topic says, its about milling threads instead of turning them.
I had the Idea first when I tried to make a thread on a 115CrV3 rod (silver steel) which turned out very bad.
The reason was the low cutting speed - wich I couldn't increase because the thread was in front of a shoulder on that shaft in the lathe.
I then thought that there must be a way to make threads with the appropriate cutting speed in order to get good surfaces.
My next thougth then was that I could mill the threads. Though for that, I would have to build a spindle for threading.
I didn't have the time to do anything and then I continued making my threads like it has been done for over a century.

After a while, I read something about thread whirl cutters and found out, that they looked exactly like I wanted to make one.

With that in mind, this afternoon I have made a cutter from silver steel. The Idea is to use it in my proxxon (like a dremel; I have modified the spindle bearing of mine so there are two bearings now instead of a single one.) instead of a single point threading tool.
It turned out to work really nice and cutting the thread was really easy because you can turn the lathe spindle as slow as you need to prevent from damaging the shoulder after the thread.
The Result is a very nice thread which has been easy to cut (and much faster as if you were cutting it with a single point tool)

There are also some advantages with that method:
- You can cut a thread pretty close to a shoulder - without the fear of hitting the shoulder since you can go very slow without getting a worse finish.
- It should give much better finish in difficult materials e.g. drill rod or similar (though the cutter would then have to be made form hss to last longer)

Cheers Florian


« Last Edit: August 03, 2017, 08:47:28 PM by Florian Eberhard »

Offline NickG

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Re: Milling threads on the lathe
« Reply #1 on: November 14, 2013, 07:06:17 PM »
Florian, great idea that for those who cut small threads in nasty materials. Nicely done  :ThumbsUp:

Offline Florian Eberhard

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Re: Milling threads on the lathe
« Reply #2 on: November 14, 2013, 09:35:37 PM »
I have just been down in the shop to make a video of the process:

<a href="https://www.youtube.com/watch?v=2jY24L9wDkA" target="_blank">http://www.youtube.com/watch?v=2jY24L9wDkA</a>

The really cool thing is that you can once adjusted finish a thread in 1 or 2 passes (2 passes if you add a finishing pass at the end)

Online sco

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Re: Milling threads on the lathe
« Reply #3 on: November 14, 2013, 09:49:35 PM »
Florian - that is definitely cool to watch!

I have the same proxxon - why have you added an extra spindle bearing - is it because of the axial float?

Simon.
Ars longa, vita brevis.

Offline swilliams

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Re: Milling threads on the lathe
« Reply #4 on: November 14, 2013, 09:51:29 PM »
Pretty cool Florian

You might find some old articles on building a thread milling attachment by J. A. Radford interesting. You can find them in his book "Improvements and accessories for your lathe" which is worth getting. It's a fun read even if you don't build his stuff.

Cheers
Steve

Offline Florian Eberhard

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Re: Milling threads on the lathe
« Reply #5 on: November 14, 2013, 10:07:16 PM »
Hi Simon

I did replace the spindle bearing quite long ago. Recently, I wanted to drill very small holes with carbide drills.
First the bearing was not so good anymore and second, the drill broke at the first touch with the material because the spindel could be moved about 1mm in coaxial direction.

I then decided to improve it and added a spindle i have made earlier for a grinding atachment (but was not used anymore):
The Spindle has a fixed bearing in the front, the rear bearing has a spring pushing the outer bearing ring towards the back. The Idea is to get a precise spindle because there won't be any bearing clearance. The principle is commonly used in grinding spindles.
The spindle is now very precise and performing really well. Drilling the holes with carbide drills workd excellent after I fitted that improved spindle.

@Steve: I didn't know that anyone had already done this!?  :D

Cheers Florian
« Last Edit: August 03, 2017, 08:48:41 PM by Florian Eberhard »

Offline garym

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Re: Milling threads on the lathe
« Reply #6 on: November 14, 2013, 10:51:40 PM »
Hi Florian,

Well beyond my capabilities at the moment but you may find this thread on a rival forum interesting:

http://www.model-engineer.co.uk/forums/postings.asp?th=84198&p=1

Gary

Offline Florian Eberhard

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Re: Milling threads on the lathe
« Reply #7 on: November 14, 2013, 10:58:01 PM »
Hi Gary

Well - the difference is that in that thread a cnc controlled machine is used meanwhile I use the lead screw of my lathe.

Cheers Florian

Offline swilliams

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Re: Milling threads on the lathe
« Reply #8 on: November 15, 2013, 01:47:24 AM »
Radford's setup is a lot different to yours. He had a spindle that ran much slower and was heavier. I think he may have aligned the cutter with the threads helix angle. Worth checking out, fun to know about :) I always enjoyed reading his stuff when I had access to old issues of model engineer. He only made tools, but was very creative at it.

Yours is fun too of course  ;)

Steve
« Last Edit: November 15, 2013, 01:51:29 AM by swilliams »

Online sco

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Re: Milling threads on the lathe
« Reply #9 on: November 15, 2013, 08:14:10 AM »
Hi Simon

I did replace the spindle bearing quite long ago. Recently, I wanted to drill very small holes with carbide drills.
First the bearing was not so good anymore and second, the drill broke at the first touch with the material because the spindel could be moved about 1mm in coaxial direction.

I then decided to improve it and added a spindle i have made earlier for a grinding atachment (but was not used anymore):


The Spindle has a fixed bearing in the front, the rear bearing has a spring pushing the outer bearing ring towards the back. The Idea is to get a precise spindle because there won't be any bearing clearance. The principle is commonly used in grinding spindles:


The spindle is now very precise and performing really well. Drilling the holes with carbide drills workd excellent after I fitted that improved spindle.

@Steve: I didn't know that anyone had already done this!?  :D

Cheers Florian

Florian,

Thanks for those details - that looks like a high precision bit of machining!

Best wishes,

Simon.
Ars longa, vita brevis.

 

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