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Recommended Lathe speed?

Specifically for turning brass

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Chris V09/04/2020 14:56:31
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209 forum posts
31 photos

Good afternoon,

Could I ask please what others would recommend as the most suitable speed for turning the brass as in the photo below. Its 1" long x 3/4" dia stock turned down to 1/4" as the small end. (The sample in the photo had to be finished with file & abrasive to get it to look that nice)

Tool bit is 1/4" HSS.

lathe speed.jpg

Many thanks in advance

Chris.

Andrew Johnston09/04/2020 15:08:48
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5410 forum posts
627 photos

I'd use 1200rpm, 1700rpm is nearer recommended but the gears in my headstock start to get a bit noisy. Not good when you live in a quiet rural village - even quieter at the moment. smile

Andrew

Mick B109/04/2020 15:10:53
1552 forum posts
83 photos

The calc I was taught at Long Eaton Government Training Centre in 1975 says 1600 rpm for HSS.

But I'd be unlikely to exceed half that.

My pension doesn't depend on cubic inches per minute metal removal, but the admiration of family and friends does on visual appeal and attractive finish.

mechman4809/04/2020 15:52:48
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2633 forum posts
408 photos

A couple of pics for you to print off & keep for ref... ref.Mechanical World Year Book 1975/76

cutting speeds 1.jpg

cutting speeds 5.jpg

George.

Chris V09/04/2020 16:04:09
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209 forum posts
31 photos

Thank you for your prompt responses guys, that confirms my suspicions as a novice.

Currently my top spindle speed is 675 RPM, my lathe being a 1930's ML1.

Clearly I'm not going to be able to run my lathe with adjustments to anything like that, so I should expect slow cutting progress and rough finish? (that's what I got)

Simplest way to increase speed I think will be to reduce the motor pulley size, something else for my to do list!

Cheers

Chris.

mechman4809/04/2020 16:08:35
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2633 forum posts
408 photos

Chris... another ref chart for you ... ref Model Engineer's Handbook by Tubal Cain 2nd edtion.

cutting speeds 2.jpg

George.

Dave Halford09/04/2020 16:12:34
698 forum posts
6 photos

You might find that has the wrong effect smiley

1000 rpm might be safer for the old girls bearings

Chris V09/04/2020 16:15:17
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209 forum posts
31 photos

Thank you George & Dave, Dave do you mean I need to increase the motor pulley size rather than reduce it?

Cheers

Chris.

Mick B109/04/2020 16:55:16
1552 forum posts
83 photos
Posted by Chris V on 09/04/2020 16:04:09:

Thank you for your prompt responses guys, that confirms my suspicions as a novice.

Currently my top spindle speed is 675 RPM, my lathe being a 1930's ML1.

Clearly I'm not going to be able to run my lathe with adjustments to anything like that, so I should expect slow cutting progress and rough finish? (that's what I got)

Simplest way to increase speed I think will be to reduce the motor pulley size, something else for my to do list!

Cheers

Chris.

Not necessarily, A sharp knife tool with a little bit of top rake, good side and front clearance (say 5-10 deg, it's not an exact matter), a small nose rad and set over to a low plan trail angle, can peel it off with little effort at low speed and leave a fine finish. I use such a tool for 90% of everything, whatever the material. I gather that it's carbide tools that need high speeds for a good finish. I do use those occasionally, but not usually for finishing and hardly at all on materials like brass.

AdrianR09/04/2020 17:01:06
439 forum posts
23 photos

Before speeding up the old girl, As Mick B1 suggested, do try using some positive rake on a really sharp tool.

Bazyle09/04/2020 17:10:14
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5139 forum posts
199 photos

I think one problem is with all manual control of the tool so it will be imprecise and jerky. I suggest the largest radius you can get like quarter inch radius. Since it is just brass you can use a bit of silver steel if you haven't got an untouched bit of HSS. However you also need the front face, ie looking from above, to be as smooth as the proverbial babies posterior.

Andrew Johnston09/04/2020 17:26:31
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5410 forum posts
627 photos
Posted by Chris V on 09/04/2020 16:04:09:

Clearly I'm not going to be able to run my lathe with adjustments to anything like that, so I should expect slow cutting progress and rough finish?

Brass is very forgiving, so it should be fine at slower speeds with a commensurate reduction in feedrate. The tool looks like it is quite pointed. Put a nice radius on the end.

Andrew

not done it yet09/04/2020 17:27:40
4503 forum posts
16 photos

With a theoretical speed ratio of 1:3 from the 3/4” to the 1/4”, Andrew’s 1700 rpm is not so far off for the average diameter! As others have indicated, either get a speedier lathe or put up with what you have. Raising the lathe’s design speed will only shorten its life - and if it has wear already....

ega09/04/2020 17:51:35
1632 forum posts
137 photos

Another point in favour of a suitable speed less than maximum is that, as you know, brass chips go everywhere and I think this will be less of a problem at the lower speed (don't know if a chip shield can be used with your Turnado).

Chris V09/04/2020 18:30:42
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209 forum posts
31 photos

Thanks very much one and all, its great to have several options to try.

Don't worry not done it yet, I was only thinking of raising the speed to what seems to be the max recommended 800 RPM...I do respect my lathes vintage!

ega, I'm just thankful that the chips from the Turnado are just that, turning brass on my faster wood lathe produces splinters that are a real pain in every sense!

Cheers

Chris.

Chris V19/04/2020 11:25:17
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209 forum posts
31 photos

Good morning, Just an update after all the helpful tips earlier about lathe speed/finish on my brass turnings with the Turnado. Speed has remained the same (waiting on a new belt) but larger radius tools sorted my issue out.

I finished the batch of cone finial turnings and just made the pair of handles shown below for my tapping tool.

I was very surprised though that the finish on leaded steel was much better off the tool than on brass.

I think an Acorn nut is next, baby steps!

Thanks once again and stay safe.

Chris.

turnado handles.jpg

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