More power/Torque for a C-3 Type Lathe

[Bob RodgersonParticipant @bobrodgerson97362]

As most who post here know I have a Tormach CNC mill. As part of the package when I went for this machine I bought the Duality lathe which is one of the siege family of lathes. This lathe has it's limitations but non the less is useable (though it doesn't synchronise spindle speeds with the mill controller so can't cut screw threads or use constant surface speeds when turning or facing).

By far it's biggest problem for me is it's low power and inability to take decent cuts on large diameter steel components without stalling and shutting down everything. A posting that John Stevenson put on this site with a picture showing him driving his mini lathe from the chuck on one of his large industrial lathes got me thinking that I could maybe do something similar.

The Duality lathe comes with an extended spindle that has an external right hand thread on it for attaching a 4th axis drive (which I have, but haven't used so far), I was thinking that I could get one of the pre-wired variable drives with a 1 H.P. motor and arrange direct driving of the spindle via a toothed belt pulley attached to the spindle using the thread and possibly the internal bore to anchor the pulley.

I don't think it would be too difficult to make this reasonably portable and with luck I would be able to keep the original motor on the lathe.

There are a couple of things I need to know before embarking on this, such as the E-Stop system. I am absolutely hopeless when it comes to electronics/ electrics, wires are just a conduit for smoke as far as I am concerned so am not sure if I can adapt the stop system that is fitted to the duality lathe 110volt motor to run on a 240 volt motor. Could this be done easily and how?

Also, with the pre wired motor system will a direct drive have the sort of torque I would expect from say a Myford Super 7 or Boxford without having to resort to using too large a pulley on the lathe spindle ?

For the type of work I have in mind for it I will not need high speeds, certainly not more than 1400 RPM, it's the torque I am in need of.

Rigidity shouldn't be a problem because the tool post on the lathe is not used, this is mounted on a fairly robust bracket that is clamped to the spindle nose, which on the Tormach is extremely rigid.

[Bob RodgersonParticipant @bobrodgerson97362]

Running the lathe with a 1HP variable speed motor.

[John Stevenson 1Participant @johnstevenson1]

Bob,

Use a 1Hp motor at 1425 revs, gear it down 2:1 to get torque and then over speed the motor via the VFD to get back to 1400.

Electrics can easily be modified to do exactly what you want.

Drop me a line, I have just the motor and VFD here.

[AjohnwParticipant @ajohnw51620]

It might pay you to use poly V for the speed reduction if you really need the 1hp and want to keep the pulley size down.

When I went through this on my lathe I thought about the speeds I tend to use and settled on a 6 pole motor to get full motor power at lower speeds but if you are setting the speed reduction via pulleys yourself it's probably swings and roundabouts.

John

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[John Stevenson 1Participant @johnstevenson1]

6 pole motors are big, heavy and expensive. Unless you are restricted to direct drive there is no advantage in using them. Pulleys are far cheaper and more adaptable.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Ajohnw on 16/03/2016 10:40:54:

It might pay you to use poly V for the speed reduction if you really need the 1hp and want to keep the pulley size down.

I've been keen to increase the top speed on my little Sharp milling machine. The VFD has been programmed to give a maximum of 50% overspeed. Despite this, the VFD was topping out at around 1800 rpm, which was the top speed with the old single phase motor. I noted that I seemed to be getting quite a lot of "wheezing" noise from the the belts, which are A sized. I'd contemplated changing to Poly V but as an interim measure I got some cogged belts and top speed is now 2800. Clearly the A size belts were absorbing a lot of power, presumably too thick for the pulley sizes and centres.

HTH,

Rod

[Neil WyattModerator @neilwyatt]

Hello Bob,

Is it brushless version of the mini-lathe?

If not, then a ~2:1 'back gear' is already fitted that you can sue as John suggests.

Or do what I did, shorten the spacer and fit a poly-v pulley around the spindle at the back (you will need to cut away a small part of the tumbler mounting casting for belt clearance) and fit a reversible two-step poly-vee pulley (smaller one is 19mm diameter) to the motor.

I don't apologise for liking to this YET again:

**LINK**

Neil

Setup before adding two-step pulley for higher torque:

[Bob RodgersonParticipant @bobrodgerson97362]

Thanks for the helpful replies. I,m out of the house just now but iwill contct JS re the motor and driver later.

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