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Cutting Speeds Table for Teach In 2014

Cutting Speeds Table for Teach In 2014

A corrected version of the cutting speed table on P.35 of Issue 216 of MEW.

Neil Wyatt09/05/2014 11:35:53
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There were two minor errors in the cutting speed table in David Clark's Teach In article in Model Engineers' Workshop issue 216.

Sorry for not spotting these earlier. A pdf of a corrected table (handy for the workshop) is to be found here:

www.model-engineer.co.uk/.../documents/cutting speed chart.pdf

Neil

Colin LLoyd17/12/2014 17:12:24
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Novice lathe/mill operator here. I note the cutting speeds from the indicated pdf - but how crucial are the speeds? Surely rounding to the nearest 10 up to 100, 50 up to 1000, and 100 beyond that is sufficiently precise and more easily set with variable speed lathes lacking rev counters. But as I said - I'm just a novice - I expect to be corrected

Tony Pratt 117/12/2014 17:28:28
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Hi Colin,

You are quite correct the figures can be rounded up or down on the M/C in question, and I am not a novice, but I was many years agowink

Tony

Michael Gilligan17/12/2014 19:07:05
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The most important part of this table is the text in the heading of the first column: Simply because it should make obvious the underlying similarity between Turning, Milling, and Drilling.

MichaelG.

.

Edit: deleted my second paragraph blush

Edited By Michael Gilligan on 17/12/2014 19:09:06

Colin LLoyd18/12/2014 15:08:43
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Michael - I'm not sure I know what you you were trying to point out. My question was regarding the necessary precision for cutting speeds. The revolution values in the table provided by Neil were precise calculations from the table's cutting or revolving distances (e.g. carbon steel = 15m/min) - which in themselves were probably gained from empirical experience rather than any theoretical or experimental work. From a practical point of view, I questioned whether the table entries could have been rounded up to the nearest 10, 50 or 100 revs/min without serious consequences to the overall finished product. I said to round up because many mini lathes/milling machines cutting speeds are based on reducing the electric motor power supply rather than on gear changes. Such motor power reduction also reduces the torque of the motor and so rounding up will help to preserve the torque.

The topic appears to be, in general, somewhat personal in that many books on lathes etc have cutting revolutions that differ to the table provided by Neil. Some books lump together cast iron, steel and stainless steel in one column and brass, bronze, mild steel in another column. So the science is definitely not that precise - so the cutting revolutions should not express a precision that is not justified. I would not tell a cook to use a kitchen measuring jug marked in 50ml divisions to add 37.25ml of vegetable stock to a recipe when there was no appreciable difference to the meal if he just added 50ml.

If there are any engineering or scientific papers regarding the basis for the different cutting speeds for different materials, I would be interested to have a link to these or pdf downloads.

JasonB18/12/2014 16:15:31
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Any table should be treated as a guide for home use, as hobby machines vary from a small X1 upto Bridgeports and beyond you should use them as a starting point and adjust to suit your own machine and available tooling.

So you could say that it is a personal thing as each workshop will be different and if you then bring depth of cut and feed rate into the equasion the variables increase three fold.

J

Bazyle18/12/2014 17:59:18
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Colin,

Re your initial question the tolerance is 50% or more. Ie it is very very vague. The speeds sort of work out ok and you can mess around according to how it seems to go. If you go too fast the tool may overheat but HSS is so much better than old carbon steel which many of these tables were originally planned for. If you go too slow it mostly doesn't matter but with a small machine you can degrade the surface finish as the tool cuts in microscopic jumps because it is a bit like pushing a big rock - once you get going it is easier if you can keep it moving.

Theoretically if you have the power and heat tolerance (ie carbide) the optimum speed advances the cutting edge at the speed of sound in the material which is at least twice these figures.

For milling cutters don't forget to allow for the multiple teeth. This is significant when you come to run a slitting saw which are often run too fast. (it is nothing like a saw cutting wood which needs to run as fast as possible for differnet reasons.)

pgk pgk18/12/2014 18:05:13
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<<For milling cutters don't forget to allow for the multiple teeth. This is significant when you come to run a slitting saw which are often run too fast. (it is nothing like a saw cutting wood which needs to run as fast as possible for differnet reasons.)>>

This is the question I was going to ask... does one roughly halve the speed for a 4 flute compared to 2 flute cutter?

Les Jones 118/12/2014 18:17:16
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Hi pkg pkg,
I do not believe the number of teeth on a milling cutter or saw have any bearing on the cutting speed. It will effect the tooth loading. If you double the number of teeth each tooth will remove half as much on each cut providing the feed rate is the same.

Les.

JasonB18/12/2014 18:23:37
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As Les says its the tooth load so with 4 teeth you can feed twice as fast as with two while keeping teh speed the same.

As for slitting saws being run too fast thats more to do with periferal speed not number teeth as you are in effect using a cutter that is 3-4" dia.

 

J

Edited By JasonB on 18/12/2014 18:26:07

pgk pgk18/12/2014 18:28:35
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Ta for the explanation,

Michael Gilligan18/12/2014 20:54:04
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Posted by Colin LLoyd on 18/12/2014 15:08:43:

Michael - I'm not sure I know what you you were trying to point out. < etc. >

.

Colin,

Just to clear any confusion:

Mine was a general observation; it was not intended as a response to you personally.

... I've only just come in, so will read the further discussion now.

MichaelG.

John Hinkley18/12/2014 21:43:12
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I was going to post this yesterday, then I thought I'd got the answer. Now, I've become confused again! So, I've bought some module 1 involute gear cutters from CTC and I'll be using them shortly to cut a number of gears for my toolpost mounted spindle. My question is: what sort of speed should I run them at? They are 50mm outside diameter, with 14 teeth. I thought I would start at around 2-300pm in my mini mill. What do others think?

Sorry if this is a thread hijack!

John

Andrew Johnston18/12/2014 22:26:02
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John: It depends upon what metal you are cutting? A few hundred rpm may be ok for brass, but is too fast for steel.

Andrew

Neil Wyatt19/12/2014 08:35:37
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There are so many variables, it's best to look at an industrial speed chart and assume those are 'absolute maximum ratings', but bear in mind three things:

  1. Small machines lack momentum and dropping speeds too far, and going too slow can increase vibration or the tendency of the cutter to stall, causing a poor finish.
  2. The tooth load is important, too slow a feed with high rotational speed will cause the cutter to rub and blunt rapidly. As Tubal Cain would say 'keep up the feedrate'.
  3. Chatter is the enemy of a good finish, if the machine/setup is reasonably rigid it can be cured by CHANGING speed (i.e. a modest increase or a decrease will usually stop it).

One tip - with small machines, if brushed on cutting oil starts to smoke, either your cutter is blunt or you are going too fast.

Neil

OuBallie19/12/2014 09:46:05
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I have never used any table, although I have them all.

I go by sight and sound.

devil

Sight:

1) The machine is ready to shaken itself to bits - too greedy with cut, depth or speed.

2) The swarf coming off glowing - speed to fast plus 1)

3) Swarf coming of in a nice long curling spiral - everything perfect, for me at least on MS

Sound:

1) The machine groans/creaks - Greedy cut and speed as 1) in Sight

2) Motor labouring - Greedy cut or speed of cut.

3) Swarf flying off in blue chips - duck, stand well clear or wear suitable clothing.

3)Something goes bang! - You now know you have reached the limit of machine or tool.

VFD to the rescue!

I now adjust both speed and feed until machine & I am in harmony, and we jig along to whatever music is blaring out over the 'net.

Geoff - What more could an old f@rt want? wink

Gordon W19/12/2014 10:08:37
2011 forum posts

Years ago I was given a tip on cutting speed- just fast enough for the cutting edges to blur into one. Sounds daft but does seem to work for lots of things, and a good starting point to try. May be something to do with the eye /brain seeing 24 shots per second ?

Colin LLoyd19/12/2014 11:19:49
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Hey guys, thanks for all the input. Everything posted has great merit and a lot of information that doesn't appear in books. As a complete novice lathe and mill operator, it has provided me with both engineering and empirical advice which will be consolidated into a single laminated page that will hang by the lathe. Such is the power of forums and I am pleased that unlike some other forums, especially those dealing with computer problems, there was not a single "go and RTFM" reply for which I thank you. You will be hearing from this novice again.

Andrew Johnston19/12/2014 11:29:15
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The trouble with using ones senses to set feeds and speeds is that instead of leading to common(sense) it sometimes leads to non(sense).

The most common cause of machine/tool vibration is too low a feedrate or depth of cut. Instinct is to reduce it further, which just makes things worse.

Andrew

Neil Wyatt19/12/2014 12:31:31
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> The most common cause of machine/tool vibration is too low a feedrate or depth of cut. Instinct is to reduce it further, which just makes things worse.

IMHO, the main cause of problems parting off.

Neil

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