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Cutting an exact diameter using a carbide tip.

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Rod Renshaw12/06/2021 19:00:16
300 forum posts
2 photos

Hi all

Any fans of Joe Pie on the forum?

I was watching one of his youtube lectures a few weeks ago and now I can't find it again. Joe was explaining how to use a "3 near identical cuts" method to turn stock to an exact diameter using a carbide tip, and get a good finish at the same time.

It's well known that a carbide tip will only cut well if it has a decent depth of cut. So the usual amateur method, when using HSS, of taking finer and finer cuts as one approaches the final size does not work at all well when using a carbide tip.

I was impressed by his method but now I can't find the video again to check I am doing it correctly! Is there a list or even an index to these things?

Any suggestions of how to find the one mentioned, I can't remember the title.

Thanks

Rod

Martin Connelly12/06/2021 19:07:44
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1848 forum posts
197 photos

On the Youtube homepage you should have a history option that will list what you have been watching. It may still be listed there.

Martin C

old mart12/06/2021 19:11:33
3312 forum posts
203 photos

If you don't have the nerve to make the last cut a big one to get the better finish, but prefer to creep up the last bit, I suggest you try using a carbide insert intended for aluminium on steel. You can take a 0.0005" deep cut with one of these on steel and get away with it.

Tony Pratt 112/06/2021 19:23:15
1643 forum posts
8 photos

What do you mean by 'exact' diameter?

Tony

old mart12/06/2021 19:39:52
3312 forum posts
203 photos

My take on exact diameter is when cutting with carbide inserts, a fairly deep cut is found to give a good finish. For instance, if a depth of cut of 0.020" is giving a good finish, and the penultimate cut gives a diameter of plus 0.040", then you will have the right size and a good finish with a final 0.020" cut. If, however, you take smaller cuts as you get near to size, the finish gets poor as the tool is not cutting at its best.

Andrew Johnston12/06/2021 19:57:57
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6222 forum posts
676 photos
Posted by Rod Renshaw on 12/06/2021 19:00:16:finish at the same time.

It's well known that a carbide tip will only cut well if it has a decent depth of cut.

Dunno where you got that from, but it's wrong, at least as a universal statement. For sure, in some materials, especially low carbon steels, the finish can be poor with small depths of cut. But in other materials, such as brass and austenitic stainless steel, the finish is much less dependent on depth of cut.

Being lazy If I need to take 20 thou off the diameter I dial in 20 thou on the cross slide, whether I'm using carbide or HSS. No point in taking multiple cuts when one will do.

Andrew

old mart12/06/2021 20:07:45
3312 forum posts
203 photos

It is a good idea to take time to experiment with cut depths on different materials to find what combinations work best.

Tim Hammond12/06/2021 20:14:56
64 forum posts

Are you sure it was a Joe Pie video? I seem to remember Stefan Goetteswinter uploading a similar topic video some weeks ago.

fizzy12/06/2021 21:25:13
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1809 forum posts
120 photos

Agreeing with Andrew, we use nothing but carbide tips - you need the correct tip for the job but anyone who telly you they have to be deep fast cuts clearly doesnt know what they are talking about! No problem taking cuts of 0.0002"

Andrew - have you spotted your deliberate error? LOL

Rod Renshaw12/06/2021 21:57:09
300 forum posts
2 photos

Thanks for the input everyone.

Martin, thanks for that, I will check my history.

Old Mart, yes that is the idea that Joe was advocating, with measurement of actual diameter ( using a tenths reading mechanical mic) at several stages to avoid the long creep up to "damn, it's under-size, and the finish is not good!" Thanks for the idea of using inserts intended for aluminium to take small cuts.

Andrew, yes I am sure you are right but I tend to use low carbon mild steel more than most other materials.

Tony, I can't remember exactly what Joe said but he normally works to sub one thou sort of accuracy, seems good enough for most model work. When I said exactly, I should perhaps have said near enough but that might have started a different debate.

Tim , I am fairly sure it was Joe, I am not familiar with Stefan's work but I will try to find the video you refer to.

Rod

old mart12/06/2021 22:10:33
3312 forum posts
203 photos

It's well worth watching all of Joe Pi's YouTube videos, he is a most talented engineer.

Emgee12/06/2021 22:16:18
2147 forum posts
265 photos

Rod

If you Subscribe to Jo Pi you can check all of his videos on his Home page.

Emgee

Mark Rand12/06/2021 22:43:18
1053 forum posts
12 photos
Posted by fizzy on 12/06/2021 21:25:13:

Andrew - have you spotted your deliberate error? LOL

 

It might be that he's got a lathe like my Hardinge that is calibrated in diameter rather than depth of cut. cheeky

 

The optimum depth of cut of a CCMT06040X insert is just under 6mm/.25" otherwise you're paying for a lot of insert that you aren't using...

 

Edit:- deleted inappropriate comment .

Edited By Mark Rand on 12/06/2021 23:00:27

Howard Lewis13/06/2021 05:57:32
5228 forum posts
13 photos

Obviously totally wrong, according to the lore, but I achieved a good finish on steel using a CCMTO6O4 insert with a 0.001" cut at low speed with plenty of neat cutting oil.

Maybe more burnishing than cutting?

The important thing thing is that it produced the required result..

Remember, according to an aerodynamicist, the Bumble Bee can't fly!

Howard

Buffer13/06/2021 08:14:43
288 forum posts
123 photos

My Harrison will take off 20 thou if you dial on 20 thou. My myford won't

Circlip13/06/2021 08:21:00
1329 forum posts

As an inexperienced apprentice, shiny finishes were frowned on by the Toolroom foreman. "Shiny means the tool is rubbing. Smooth grey means it's cutting"

Regards Ian.

not done it yet13/06/2021 10:10:15
6270 forum posts
20 photos
Posted by Buffer on 13/06/2021 08:14:43:

My Harrison will take off 20 thou if you dial on 20 thou. My myford won't

I find this unbelievable. How many 20 thou cuts would you need to take to remove 200 thou with your myford?

John ATTLEE13/06/2021 10:30:49
13 forum posts

Dear All,

I know that, in theory, my Denham DL6 with plain headstock bearings and very low RPM should not benefit from carbide insert tooling but it certainly does! I use a combined tool post and tool holder and this means that the cutting tool is always at the right height. Obviously, I run it in top gear unless the work is more than about 3" in dia.

I can turn or bore to about a thou. The machine is fitted with a three axis DRO system which I think is essential to make up for my limited skills. I use three passes to eliminate 'spring back' and obtain a consistent size to be measured. Thereafter, the DRO displays the correct dia, after three passes have been taken. I would not hesitate to advance the tool just a thou.

I certainly achieve good enough results for my automotive work. I very rarely use HSS cutting tools in the lathes now.

John

Buffer13/06/2021 10:41:31
288 forum posts
123 photos
Posted by not done it yet on 13/06/2021 10:10:15:
Posted by Buffer on 13/06/2021 08:14:43:

My Harrison will take off 20 thou if you dial on 20 thou. My myford won't

I find this unbelievable. How many 20 thou cuts would you need to take to remove 200 thou with your myford?

I think your missing the point.

Andrew Johnston13/06/2021 11:37:27
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6222 forum posts
676 photos
Posted by fizzy on 12/06/2021 21:25:13:

Andrew - have you spotted your deliberate error? LOL

I wondered when someone would fall for that one. smile

As Mark says, on my lathe setting 20 thou on the cross slide means 20 thou off the diameter, not the radius.

Andrew

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