The range of speed should be good for turning aluminium.on my bench lathe (Emco compact 8) I use 1700 rpm for most of the time. I reduce speed only if the diameter of the stock is on the large side. What is the problem you are having? The set up mentioned in your post uses DC brushless motor. You will need to replace the existing motor which is not a trivial task

A pic of your lathe and it's setup?

Having 6 speed steps suggests you have a countershaft setup. I wonder if all you need is a different pulley combination driving it.

If only it were! It's clearly a 4 pole single phase induction motor. Probably overkill to convert to 3 phase with vfd if this would be the only job needing the low speed. As Pete mentioned a smaller or larger pulley somewhere in the drive might be the best approach.

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I have taken the liberty of grabbing that image [duly credited] for the convenience of those following this thread:

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MichaelG.

Looking Taig's website, their step pulley sets are less expensive than I imagined. If these are available from Peatol, reversing one of your existing pulleys and inserting a new one on an overhung countershaft seems the simplest answer, as machining new pulleys on the lathe would run straight into the original problem.

A Google search for "Taig Countershaft" brings up a few designs. (Assuming that your current setup looks like this picture on the Taig website).

Brian G

435rpm is good for aluminium being cut with HSS at anything up to Ø110mm, you would only need to go slower for a larger diameter or another material. I think Andrew is correct, you need a new expert.

There are plenty of feed and speed tables and calculators you can use, it would be a good idea to use one of these and learn from what has already be found by others rather than muddle along, trying and failing and not knowing what is going wrong. A feed and speed calculator will allow you to eliminate one thing from your machining process so if you still have problems it is one less thing to think about.

If you look at the top of this page there is a black bar with a link labelled workshop on it. Hover over this and you will see processes. Follow this and you will find amongst them a link to a section on feeds and speeds that would be a good place to look at what has been discussed before on this subject.

Martin C

PS. When an RPM is given for a milling tool it can also be used for a workpiece in a lathe. The rpm figures for a Ø50 milling tool are the same as the RPM figures for a lathe workpiece. So an rpm given for a Ø50 HSS tool cutting aluminium in a milling process is the same as the rpm for a HSS lathe tool cutting a Ø50 aluminium workpiece in a lathe.

Edited By Martin Connelly on 10/01/2022 10:08:12

I thought the same, because the range of speeds available is sensible for lathe specialising in small diameters.

But DrMC's second post hints at an interrupted cut on a largish diameter: 'I was trying to cut a step in Soft Jaws so that I could mount a steel disk that was too large for the jaws of the 3 jaw chuck as supplied.'

Assuming I've understood, which is always doubtful, I would approach this job by making a stub mandrel and supergluing the steel disc to it. The 'stub mandrel' is just a short length of rod that fits into the chuck, and faced off to provide a nice flat surface for the glue. The mandrel is removed by gently heating it with a blowlamp or boiling in water to destroy the bond. An remaining glue is cleaned off with Nail Varnish Remover or Acetone.

Clockmakers substitute a hard wax for superglue, and although the bond is weaker, there's an advantage. The wax is melted on the end of the mandrel and the steel disc centred roughly on it, then, with the lathe spinning, the disc can be accurately centred by nudging while the wax is still soft.

Never tried wax myself: I suspect the need for speed whilst centring requires skill and practice. Superglue is easy but joints are severely weakened by moving while it sets, and it grabs too quickly to allow nudging.

Going back to the 'plug and play' question, how about an industrial sewing machine motor with controller? Something like this JACK JK513A Energy Saving 550W Servo Motor currently on ebay from a UK supplier.

Dave

I would use the following values, for HSS tooling:

Cast iron: 60fpm for castings, higher for continuously cast

Stainless steel (austenitic 3xx series): 80fpm

Low carbon steels: 100fpm

Brass: 300fpm

Aluminium alloy: 600fpm

However, none of these values are critical, and there are other factors that need to be taken into account. I don't calculate an exact value, but just do a rough calculation in my head. In general HSS tooling is more forgiving than carbide when it comes to the range of cutting speeds. There are no right and wrong answers. Even those in the professional literature are only guidelines.

Andrew

Rather than faff about with pi and inches after looking up a materials Surface Speed in feet/minute, I prefer to start with a simple easy to remember approximation that does away with all the hard sums, hurrah.

It is:

RPM = 10000 / diameter in mm

This happens to be about right for HSS cutting carbon steel. Thus a 25mm diameter steel rod would be spun at about 400rpm, and 5mm diameter at 2500rpm.

Other materials are simply proportionally faster or slower than ordinary steel:

• RPM for cast-iron and stainless is Half steel RPM
• RPM brass is one and a third steel RPM
• RPM Aluminium is twice steel RPM

If using carbide rather than HSS, multiply the HSS result by 4 to 6. (If your machine can deliver the necessary power and speed. Otherwise, as fast as it can manage.)

Be prepared to experiment. Much depends on what you're doing and the limitations of your set up. Starting with the estimated RPM, adjust depth of cut and feed rate for best results. If you get problems like chatter, poor finish, or overheating, play with RPM as well. Don't expect a hobby lathe to work at industrial production rates! With HSS it's usually OK to reduce RPM a lot. Carbide run too slowly and with insufficient depth of cut may not produce an acceptable finish.

I run my machines so they sound loaded but aren't labouring. Sounding OK and producing an acceptable finish are more important than sticking religiously to the estimated RPM. The estimate is a good starting point, not a guarantee.

Dave