Axminster M950 and Supernova Chuck Problems

[mudman]

Hi all,

First time back here for a while and now I pop up again with a problem. :roll:

Haven't been doing a lot of turning lately but recently I've been looking at the lathe and realising that I need to get back on it.

Anyway, I was always a bit dubious about the accuracy of my Axminster M950 lathe but recently using the scroll chuck and pin jaws, it was obvious when I mounted the workpiece that there was a considerable amount of runout. I've always known it was there but for what I wanted to turn, it made things very awkward.
So, I've had the chuck apart, re-mounted the jaws, cleaned everything up and still no different.
I then had a look at the junction between the chuck and spindle shoulder and noticed a gap. This I thought would be the reason and so made a rough washer out of mdf and tried again. Even worse this time with the runout plainly visible when rotating.

So, I've had a good look at things and this is what I've come up with.

• 1. The jaw slides seem a little loose on the chuck and can be moved back and fore by a small amount. (less than half a mm I guess).
  2. There is a small amount of damage to the chuck insert's external thread that screws into the chuck body.
  3. The internal thread of the insert seems to be different to the spindle thread. When you put it on partway, there is a considerable amount of 'play'. The manual says the insert thread (Type D) is a 1"x8tpi UNC thread. However, checking with a whitworth thread guage I have, it gives a perfect match to the 1x8 whitworth.

Has anyone got any advice on this?
My prime suspect in this is the insert being a different thread to the spindle although I am a bit unsure whether there should be that much play in the jaw slides. Can anyone confirm if this is usual?

Thanks in advance.

 

[Blister]

I would check with Axminster what 1"x 8 tpi it is ?

You need to get the chuck running true before goung anywhare else :wink:

 

[TEP]

Hi Barry, sorry to hear about your problem.

I believe it is normal for there to be a small amount of play in each jaw mount. .5mm or slightly less would be right I think.

As to the 1" x 8tpi, whether it is UNC or Whitworth I can't help. Normally the spindle thread is slightly loose until the insert fits over and locks onto the register of the spindle. It is the register that centers the chuck.

I think you may be correct in saying that it could be the insert causing the problem.

 

[mudman]

Thanks for the replies.

Just had a chat with the chap in technical services and he is insistent that the thread on the spindle is UNC which would be more sensible than Whitworth. Although, that thread guage did match the thread exactly so, I dunno. :?

He did say that it is normal for a bit of play as the chuck screws up, but this does seem excessive to me.

Seems to me that the problem is with the insert. It seems to go tight on the short unthreaded portion after the thread on the spindle. I'm thinking that it might not be screwing all the way down due to this.

 

[TEP]

Hi again Barry.

You said

Seems to me that the problem is with the insert. It seems to go tight on the short un-threaded portion after the thread on the spindle. I'm thinking that it might not be screwing all the way down due to this.

That short un-threaded piece is the spindle register, the insert should slide over it and lock up against a small shoulder. If you look inside the insert you will see the first few threads have been machined away to allow this.

It is not that unusual for the register to be slightly over size, I have seen it when the club I am a member of bought 3 new lathes. All the registers needed work so the S-Nova inserts would go over and lock.

What one chap did was to use a HSS scraper and VERY GENTLY scrape away at the register dia. until the chuck fitted. I'm not advocating this without actually seeing the problem, but it worked for him.

 

[mudman]

Hi again Barry.

That short un-threaded piece is the spindle register, the insert should slide over it and lock up against a small shoulder. If you look inside the insert you will see the first few threads have been machined away to allow this.

It is not that unusual for the register to be slightly over size, I have seen it when the club I am a member of bought 3 new lathes. All the registers needed work so the S-Nova inserts would go over and lock.

What one chap did was to use a HSS scraper and VERY GENTLY scrape away at the register dia. until the chuck fitted. I'm not advocating this without actually seeing the problem, but it worked for him.

Ah, I knew it had a name.
That would make sense and it would go along with my other experiences of this lathe and make me think 'typical'. I would more readily believe that the chuck has been correctly machined rather than the lathe. I've not been impressed with the overall quality of it and at some point would like to upgrade to a better make that isn't imported from China.

I think I may have a go at a bit of modification this evening, I like the idea of the HSS scraper. Do you know if the tolerances on the register are critical in anyway?

 

[TEP]

The register is used to centre the chuck, so should be machined with JUST ENOUGH clearance for the insert to slide over until it butts against the shoulder. Hopefully a engineering type may come along and give you a better idea than I can.

All I can say is, if you try it yourself be very careful as it is used to center the chuck. If you mess it up the chuck could be well off centre. As with wood turning cuts, small and often is all I can say.

PS - It is possible that it could go with just a bit of judicious use of emery cloth, or a very fine file. A bit Heath Robinson, but I can't think of any other way, Unless you have the insert machined, and how you would center that in a lathe I've no idea.

 

[CHJ]

Barry have a look at this List: (T04M)

If you have the means (micrometer or vernier calipers) check the dimensions of the spindle register and the insert, there should be just enough difference in spindle and chuck socket sizes to allow a sliding fit. ( (a couple of tenths of a thou)

If they are exactly the same size you won't be able to screw the chuck on.

It is up to you when you determine which is incorrect as to what you do, if it is the insert that is incorrect and you never intend fitting a different chuck then reducing the spindle is fine.

 

[mudman]

I thought it might be important. I suppose that modifying the spindle could have the potential for a disastrous mistake.
I'll check out the sizes (thanks Chas) and see what they are. If it's the insert than I think I'll see if I can order a new one.

 

[mudman]

Okay, I've done some measuring.
The spindle register is definitely over size and tapers slightly up to about 4 thou over an inch at the shoulder. So there is no chance that it can but up against the shoulder.
I have mad things a bit better by removing some burred edges from the insert but have shied away from modifying the spindle yet. I think I may try to find a local metalworker who can take a few thou off the spindle for me.
It is very annoying though.

 

[CHJ]

Barry, for the removal of just 4 thou. you can do it yourself in situ with some abrasive.

Start with say 180 or 240 grit and polish it with finer when you get to size. It will come off quite quickly.

Use a steel rule or the blade of a wide flat scraper to back your abrasive and with the lathe running at 4-500 rpm gently dress it off. Try to remove the taper first and check regularly.

Wipe off any abrasive dust before trying a fit, to stop things binding up.

IMO that would be better than dismantling the machine, and it would have to be someone with good metal turning skills or a good spindle grinder setup to get the existing spindle running true to start with and do any better.

 

[mudman]

Barry, for the removal of just 4 thou. you can do it yourself in situ with some abrasive.

Start with say 180 or 240 grit and polish it with finer when you get to size. It will come off quite quickly.

Use a steel rule or the blade of a wide flat scraper to back your abrasive and with the lathe running at 4-500 rpm gently dress it off. Try to remove the taper first and check regularly.

Wipe off any abrasive dust before trying a fit, to stop things binding up.

IMO that would be better than dismantling the machine, and it would have to be someone with good metal turning skills or a good spindle grinder setup to get the existing spindle running true to start with and do any better.

Thanks Chas I think I'll try that.
You know it's at times like these that I really regret not spending some more timewith my father and learning just a fraction of his extensive metalworking skills. He would have been able to sort it out in an impressively short period of time.

 

[wasbit]

I'm not an engineer but here's my take on the problem.

Btw, what make is your chuck?

Anything threaded onto the spindle will be a really sloppy fit until the register comes into play. If it wasn't you would struggle to get things on and off. The same applies to the jaws on your chuck, if that play wasn't there you would have great difficulty moving them.

On some lathes the register (no.2 in the diagram) is 'relieved', ie a lesser diameter than the threads and therefore can no longer do this job. The back, vertical face of the spindle then becomes the register removing any play in the threads and making the chuck run at 90 degrees to the bed (as Tep has already said).

You say there is some damage to the chuck insert threads. Are you sure that it has the correct insert for your lathe? Even with a heavy chuck once the threads have started it should be easy to spin it up to the register. If you bought the chuck 2nd hand you might have been told a fib or if new, had an unlucky mix up.
I wonder if you are correct in your assertion that the insert is 1" bsw (British Standard Whitworth) because that also has 8tpi but a different thread form.

Tracy Tools - http://www.tracytools.com/variousassorted.htm or any engineering supplier should be able to sell you a 1"x8 unc tap (£6 + p&p) but if your insert is 1" bsw don't try retapping it to 1" unc, buy a new insert. You may find that the chuck then screws all the way on.

Use your local Yellow pages to find engineering suppliers then be cheeky and take your chuck to them and ask if there is any way they can tell you the thread size.

Ask if there are any model engineers locally etc. They tend to be quite friendly because they are hobbyists like us.

Find a local woodturning club to attend. They normally have at least one member who is in engineering.

 

[CHJ]

Welcome to the Forum wasbit

On some lathes the register (no.2 in the diagram) is 'relieved', ie a lesser diameter than the threads and therefore can no longer do this job.

This relieving is 'normally' only a percentage of the register or just in front of it to allow the fitting of a locking screw in the chuck rear flange or adaptor to secure it for reverse turning.

Tracy Tools - http://www.tracytools.com/variousassorted.htm or any engineering supplier should be able to sell you a 1"x8 unc tap (£6 + p&p) but if your insert is 1" bsw don't try retapping it to 1" unc, buy a new insert. You may find that the chuck then screws all the way on.

If there is still doubt about the thread form (damaged or otherwise) I'd be tempted to take the insert to a local lathe stockists and try it on another spindle.

Mind you a tap to the same form as the spindle thread has its uses for temporary wooden chucks, faceplates etc. however when they get up to 1-1/2" in HSS at something around £120+ each they are a bit of a luxury

 

[CHJ]

Opps deleted by chas

 

[mudman]

Wasbit, welcome to the forum.

The chuck is a Supernova
I have been told now that it should be a sloppyu fit, it's just that my particular sloppy fit is really sloppy which led me to suspect the thread.
It is definitely the correct insert, I have checked this and it was bought new.
I really can't tell if I am correct about the BSW bit, all I have is an old thread guage that I bought in a market ages ago and not being an engineer, I can't be sure I am correct. The guage did match the thread exactly though. I'd like to try a UNC guage against it but haven't got one of those. According to Axminster it should be UNC, whether it has had an incorrect thread cut or not, I can't really tell for certain.

I think now that the main culprit in all this is the register being oversize. it is actually about 4 thou bigger at its widest that means that the insert cannot physically engage with the rear face. I'm going to have a go at modifying this part of the spindle with some judicious abrasive use as Chas has outlined above.

I do actually have a 1 x 8" BSW tap. I bought it ages ago intending to try making temporary chucks and such like but never got around to using it. I'm going to put a thread into something with it and see how it fits onto the spindle thread. May give some insight and if it fits, well I have another tool to use.

 

[CHJ]

Barry, Just for interest and of no help with the chuck, you may be able to see the difference if you place the tap along the spindle thread, the difference between 55 and 60 deg is not that obvious especially when the root and crown radiuses are taken into account. That is if the tap leading threads aren't too long.

As to the differences in thread form, This reference gives most of the figures

Some Whitworth and UNC threads will mate, danger is as pointed out in the above that if they are taking critical loads the load is not taken at the designed mean diameter and may fail.

 

[wasbit]

[/quote]This relieving is 'normally' only a percentage of the register or just in front of it to allow the fitting of a locking screw in the chuck rear flange or adaptor to secure it for reverse turning.[/quote]

On mine, a Draper WLT 90, it is relieved the full length between the threads and the shoulder.

Looking inside my chuck, the thread crowns provide the smallest bore with the mouth of the adaptor being a much larger bore. If the chuck didn't screw on far enough for the vertical faces to meet, I doubt if it would ever run true.

Box is normally recommended for taking threads but if you could find a chunk of scrap aluminium, that would make an ideal test for your tap.

 

[CHJ]

This relieving is 'normally' only a percentage of the register or just in front of it to allow the fitting of a locking screw in the chuck rear flange or adaptor to secure it for reverse turning.

On mine, a Draper WLT 90, it is relieved the full length between the threads and the shoulder.

Looking inside my chuck, the thread crowns provide the smallest bore with the mouth of the adaptor being a much larger bore. If the chuck didn't screw on far enough for the vertical faces to meet, I doubt if it would ever run true.

That is far from Ideal wasbit, in essence the spindle nose is ensuring that you chuck is square to the spindle but you are having to rely on the threads seating centrally on their respective forms for true running, and hopefully not sliping if you ever get a catch etc. not something I would like to trust 100%.

 

[wasbit]

[/quote]That is far from Ideal wasbit, in essence the spindle nose is ensuring that you chuck is square to the spindle but you are having to rely on the threads seating centrally on their respective forms for true running, and hopefully not sliping if you ever get a catch etc. not something I would like to trust 100%.[/quote]

Agreed, but I don't want to belabour the point because it's taking the focus away from helping mudman.
Suffice to say that both the lathe and chuck are commercial products that are 'as bought', that's the way that they fit together and I can't really do much about it. (That's not meant to sound as nasty as it reads)
I presumed this was quite common for hobby woodworking lathes as I think the spindle nose on my old Record was the same.

Btw, what's a catch? I've never caught anything yet as I'm too busy ducking, though I might get it on the third bounce.