Not a Pultra 17/50

Hi all

I recently purchased what was supposed to be a Pultra 17/50 50mm centre well it arrived today and what a bonus it turns out to be a 17/70 looks tatty but the headstock is very smooth and no play although I am going to strip it and paint in original colour just waiting for a manual to turn up from Smart & Brown.

17/70 pictures

Useful bonus getting a 17/70

MichaelG.

Wow, looks good!

I thought I knew the Pultra accessory range, but I'm not familiar with the item shown in the second picture. Some sort of tailstock?

Andrew

Yes it’s a tailstock and I had not seen one like it before either, screw feed MT 1 .

Dell

That certainly is an unusual tail stock, I can't see anything like it in any of my Pultra parts catalogues etc.

I don't think it looks like a Pultra part that's been modified either, but it looks nicely made and fit for purpose (as far as I can tell from the photo) , so well done, you'll not regret buying a Pultra ! I believe I've got eight, at last count, they may be breeding ?

The compound slide looks a bit modified, but as long as it's functional, who cares. Someone must have done it for a reason.

Hope you enjoy using it, I'm sure you will.

What you need now is a nice Mardrive or similar motor/countershaft arrangement.

Colin

I haven’t got the room for a Mardrive but I do have a Multifix motor that should do the job, I spoke to Tony at lathes.co.uk today and sent him a picture he said he hadn’t seen the like before either it’s a screw feed with a MT 1 taper he wants some pictures when it’s restored.

I was hoping my Derbyshire Magnus collets would fit but although they fit the headstock the drawbar only just starts to thread onto the collets so I am on the lookout for some more Pultra collets.

colin as you have a few Pultra lathes have you one with a quick close if so how the hell does it work ?

Dell

That's a good question, I'll have to go and have a look in the morning. I've only got one with the quick close lever on the headstock. Just to muddy the water, that one is a 1770, but with the large bore headstock, it is listed in the catalogues of the time, it takes the 20mm collets, same as the 1590 models. Think they are 19.7 mm by 1.666mm pitch. Much like Schaublin W20 collets.

The Mardrive doesn't take up much room if you can arrange it into a cabinet and fit it underneath the lathe.

Or in one of the under drive cabinets that Pultra sold, with drive to the left, drawers on the right, and room for your legs and the clutch pedal in the middle, quite neat.

Colin

Hi Colin

i have only just enough room for my legs under the small steel bench I will be putting it on , I think you will find that the W20 Schaublin will fit the 15/90 as I spoke to Chris at Smart & Brown and he said that the Schaublin 10mm and 20mm will fit the 17/70 and 15/90 respectively.

lf you could have a look at the quick close that would be great because I can’t work it out , I have ordered a manual from S&B but it’s not arrived yet it may explain it it.

Thanks Dell

Edited By Dell on 01/12/2021 20:34:54

I've got a couple of 1750 headstocks fitted with collet closers. I'll have a look tomorrow evening and figure out how it works. Current assumption is that something goes slightly over-centre as the collet grips. My collet closers look like they are intended to be used without stopping the spindle, as one would expect.

Andrew

Had a quick play this morning. As expected there's an over-centre lock. Here's the headstock and collet closer in the open position:

As the vertical bronze lever, on the left, is moved to the left it comes up against resistance. With further movement it 'clicks' over and locks. The locked position is shown here:

I suspect that the over-centre lock is provided by the linkage under the lever and yoke. I don't know if my example is worn but everything is very loose in the open position. But it still seems to close and lock properly. Under the brass cap over the spindle nose there is a finely knurled bronze ring. I expect this is used to set the position of the collet so that it closes properly within the small amount of lever movement. The closer will definitely operate with the spindle running.

Andrew

Dell

To power the Pultra I would recommend one of the Industrial sewing machine motor kits being offered on "the Bay" and especially the one made by Jack. The kit has a powerful ( 3/4 HP) brushless DC motor, with mounting components and includes the motor electronic drive unit similar in function to a VFD and all for circa £100. The kit is truly "plug and use" with no wiring up needed. The motor can be mounted in an under drive configuration, as it is usually fitted on a sewing machine, or behind the machine. Interestingly the Mardrive unit was originally designed and used on industrial sewing machines and I believe the stand the Pultra was offered on was also derived from the same.

I have my sewing machine motor mounted on a bracket just behind the headstock and have used a VB 8x375Li belt to couple it to the spindle pulley. There are pictures of my set up posted on the ME site. The motor can provide extremely high torque even at low speeds so a countershaft arrangement isn't really necessary. If an overhead drive arrangement for milling/gear cutting etc is needed then just buying a separate motor is probably easier and since the motor is so small , about 100mm cube, it could be mounted on the overhead drive column.

The only downside I have found so far is that speed control algorithm of the drive unit is designed for sewing machines and from the OFF position goes to a fixed low speed setting ( can be preset to between 100 and 200 rpm) before moving through to a linear speed control region that goes from the low speed setting to the max speed which can also be pre-set up to 4000 rpm. I've changed the motor pulley to a smaller one that matches the Pultra spindle pulley to limit the max spindle speed to 4000 rpm as the original motor pulley would have e driven it at 8000 rpm on max motor speed obtainable. I'm not sure what the max spindle speed is for a plain bearing Pultra but I'm sure the ball bearing head is rated to beyond 8k rpm.

Another feature of the motor drive unit is that it provides servo speed control so the motor can accelerate and decelerate to the set speed demand vey quickly and the speed doesn't vary much with load. Not much of an issue with a direct spindle drive coupling and collets but could be if using a high inertia countershaft system and a big chuck.

I've found that the Brushless DC are exceptional performers and have recently "upgraded" my Bergeon 30535 watchmakers lathe base and motor unit with a BLDC motor to replace the noisy, dusty and smelly brushed AC motor. The BLDC motor runs virtual silently and there is no smell of ozone or carbon dust generated by the arcing brushes as a plus. To do this I used a BLDC motor controller used for electric bikes and COTS 24V DC power supply module. All low voltage and safe to wire up and the EV bike controller is better in that it can control speed from zero to max speed in a single linear range.

I'm also thinking of doing the same to a Bergeon Multifix motor unit which is equally noisy and has very poor variable speed control which it does by moving the position of the brushes with respect to the stator.

There a some tiny 2kW ( 3HP ) BLDC motor available so I might try fitting one to my Colchester Chipmaster !!!

Clive

Hopefully these drawings etc will help, but your manual from Smart & Brown should be much clearer.

My first attempt at uploading pics, so this may go horribly wrong.

Having read the manual after posting I realised that I was wrong about setting the collet position. Should have read the manual before posting.

Colin has saved me from needing to scan and post the relevant pages.

Andrew

Hi Andrew

i think that makes sense but just to get it straight in my 70 year old head the collet and drawbar are screwed together as normal the quick close just closes the collet to grip the work.

Thanks for your help Dell

Hi Colin

yes I think my Multifix motor is noisy as well even though it had new bearings 6 months ago , I tried a sewing machine motor on my Derbyshire but found it rubbish, but I think you are on about industrial sewing machine motor,I was going to try one but then this Multifix came up but will have a look because I can always sell the Multifix for good money, not heard of the BLDC motor do you have a link to it ?.

164092634362
is this the motor thanks Dell

Edited By Dell on 02/12/2021 17:33:32

I don't have any experience of Multifix motors, or brushless dc motors either, so can't help on that, sorry.

Colin

I've had another look at both of my collet closer headstocks, this time with the manual open at the adjustment page. It's not clear that there is an over-centre effect. The closure just seems to rely on friction from a spring loaded ball in the handle, on the extreme left, on serrations on the spindle.

The way I read the manual is that the handle, extreme left, is rotated to close the collet onto the work and is then locked in place. The vertical handle then simply opens the collet or closes it to the pre-determined place. Probably the best thing to do is look at a real unit while referring to the first and third photos posted by Colin.

Andrew

My Pultra isn't running yet, but I have bought a 1/2hp 3-phase induction motor and VFD, which I expect will be fine. This will be driving the headstock, and accessories, via a baseplate and multiple pulleys behind the lathe. I have an original motor with clutch, but there is no plan to use it.

Andrew

Sorry Colin that post was aimed at Clive just used the wrong name.

Dell