Union Lathe .... Help !!!

[Darren]

I hope someone can help me here as I'm banging my head a bit too much for my liking this last couple of days.....  


I've set up my Union Lathe to cut a 6 tpi thread. It's got more than enough power even though it's only got a 1/4hp motor on it. That's not an issue, in fact I stopped using the slow speeds as it cut nicer if it was run a little faster.

The problem I'm getting is creep, very time I take another deeper cut the tool tip has moved forwards. This of course is a disaster when cutting threads. But I just can't figure out what's causing it? I mean gears are gears and they sould keep a constant relationship with the leadscrew, but something is amis.

The leadscrew is engaged with a dog clutch so can only go in the same spot every time so it can't be that.

This is the lathe, In fact this is "THE" lathe .... the very same one .... http://www.lathes.co.uk/harrisonwood/page7.html

[tinkerer]

The tool is moving in relationship to the work, or the work is moving in relationship to the tool. Does the spindle have end play? Is the tool moving on the tool post? Is the compound changing the angle? Every moving part involved will have to be verified as stable, from the lead screw to the spindle and everything inbetween. It will take patience and perseverence. A process of elimination.

[sbwhart]

Darren

Give the tool a good run up to the work to take all the back lash out of the system.

Good luck

Stew

[Darren]

I'll have another go this week.

It'd be a shame if I can't sort this out as it's cutting this 6tpi thread in it's stride with either normal low gear or any of the three back gear ratio's.
The dog clutch is nice to use as well, no need to have a reverse on the motor.

I've set the gearing up to give me 25, 50, 101, 157, 314, 628 and found the 25rpm to be too slow, even for threading, well this thread at least. Maybe more use on a larger diameter.

One problem I am getting is the pulley wheel "welds" itself solid to the spindle when I use back gears, but I think I have that sorted now .... too much pressure from the drive belt causing metal "pick-up" jamming it solid.

Still, like I said, not given up yet just looking for ideas .... I'll try a longer run in to the work Stew .... 

[Darren]

I think I've sussed the problem, rather silly of me really but we live and learn ....  

The leadscrew handwheel, like much of the other parts, is fixed to the screw with a drift pin. When disassembling the lathe to clean it up I managed to get all the pins out easily enough but I could not get any of them back in. The diameters were just too large. I even ground a taper on the ends to help but still they would not go back.

Anyway, when I put the leadscrew handwheel back on I hammered, soft headed leaded mallet, and it was really tight. But I left the pin out and forgot all about it. The wheel has moved to the left which now allows the leadscrew to creep too the right.  

I feel so silly now ...   I'll sort this out and have another go, prob tomorrow as I'm busy today.

Thanks for letting me blather, helps the thought process .....  

[bogstandard]

Sure they aren't tapered pins Darren, and you are trying to fit them in from the wrong end?


John

[Darren]

Good point John, I'll measure them later and get back on that one ... 

[Darren]

Got a chance to have a look, yep taper pin ....  Thanks John 

However, didn't cure the problem .... so wasn't that.


I'm now thinking that it has something to do with engaging the dog clutch at the wrong place?

When I first tested cutting a thread I tried 8tpi, which is the same pitch as the leadscrew. So after taking a cut I could dis-engage the leadscrew with the dog clutch, wind the carriage back and re-engage the lead screw. Of course as I was cutting an 8tpi thread and the leadscrew is also 8tp then one turn of the leadscrew matched one pitch of the thread being cut. Simple and easy.

But when I cut a 6tpi thread one turn of the leadscrew does not match the pitch of the thread being cut. At least that's where I'm beginning to think the problem is?

I'm not sure how to get around this, leave the lathe leadscrew engaged and reverse the lathe? That would be a monumental PIA with no reverse power. But would it work?


And what about all the other threads on the threading chart, do they also need the leadscrew left engaged?

Me thinks me needs a reverse ..... poo 

[sbwhart]

Has it got a threading dial ?, if it has drop in the same number each time, If not you may have to use the old trick of marking the position with chalk wait for the chalk marks to line up and then drop it in.

Hope this helps

Stew

[Darren]

Hi Stew, No threading dial, the leadscrew will only drop in at one point no other option.

What's this chalk thingibob....

[Darren]

A little clarification,

The carriage cannot be disconnected from the leadscrew, it's a permanent engagement. What you do is operate the lever at the left hand side of the leadscrew under the headstock to engage and dis-engage the leadscrew. (what I call a dog clutch?) It only has one point of engagement.

[andyf]

Darren, have you been using the dog clutch to disconnect the drive from the leadscrew so you can manually return the saddle ready for the next cut?  That would work for cutting an 8 TPI thead (the same as the leadscrew), but not for 6TPI. You can use single-point dog clutches to pick up threads, but they need to be at the start of the gear train, not at the end of it (he said authoritatively, having just looked it up in Martin Cleeve's book on screwcutting, without entirely comprehending it).

Andy

[sbwhart]

Two mark in line, one on the chuck the other on the spindle bearing housing where you drop it in, mark or set the start position of the saddle, take your cut, take it out of gear, put the saddle back to the same start position, wait for the chalk marks to line up drop it in, and you should be in pitch.

Stew

[Darren]

Thanks guys, that makes sense ... I'm only guessing but something like every third turn or sumut would be in line? I'll give it a go in a mo 

[tinkerer]

I didn't even consider that you had said you were disengaging the lead screw and moving the carriage. The picture shows a handle on the lead screw on the right hand end. Can you not use it to return the carriage to the start point? Do you have to disengage the clutch dog before returning the carriage?

[Darren]

Hi, Tink, I don't have the strength to wind it back with the leadscrew handle when in gear.

Here is the lathe,



The belt is not in line, it all moved about as it settled so i will re-do that



I managed to cut a 6tpi thread of sorts, it's dog rough but it is 6tpi !!
In the end I wound everything back with the large countershaft pulley, not much fun but it proved leaving everything engaged works. I'm still not sure I'm going to manage with this lathe, the finish is nowhere near good enough. Too much backlash for a start and the top slide has a really crude mounting which doesn't help.

But it is a 6tpi thread. I'll have a bit more of a try and see if I can improve the finish. What keeps me going is the fact that this lathes cuts this thread easily, the swarf just curls off nicely. But the whole lathe needs refining and fettling to make it sweet regarding slop.



Still, it's a good feeling to get this far, esp with a lathe so old ...... anyone got a Colchester Student they want to sell ... that's the lathe I think I would really like next. 

[spuddevans]

Hi, Tink, I don't have the strength to wind it back with the leadscrew handle when in gear.

Is there a way to perhaps attach a drill temporarily somewhere to power the reverse pass? 


Tim

[bogstandard]

Darren,

Have you had a good look around the change gears area, a lathe with that sort of setup usually has some sort of tumbler reverse, to reverse the leadscrew.

It does seem very strange for something like that not to be on the lathe.


John

[Darren]

John, I'd not even considered the tumbler. Though it's not the best design it's worth considering.

They could have put a handle on it !!!

[Darren]

A handle on the countershaft would do it, it would then be geared to help  ...... mill a square on the end of the shaft and use a milling vice handle.

Or drill and fix a handle to the large pulley. Not sure about drilling it though in case of weakening it. It's cast iron though so I guess would be OK?

[andyf]

Darren, when you are winding it back by hand using the big countershaft pulley, the relative sizes of that and the motor pulley means that you are fighting the ratio and trying to turn the motor much faster. Is there a quick and easy way to slacken off the belts between cuts? Loosening the one from the c'shaft to the spindle would be best, because you could then just turn the leadscrew handle (if there is one) with a bit of gearing down (8:6) between it and the chuck. If no handwheel, turn the chuck by hand, taking care that it doesn't come unscrewed from the spindle - OK, the ratio from spindle to leadscrew is uphill at 6:8, but that shouldn't be hard if you eat your breakfast Weetabix.

Looks to me as if this lathe is crying out for half-nuts, rather than a leadscrew which is permanently engaged to the saddle. 8 TPI is a very common leadscrew size, so maybe an old set of half-nuts from another machine would trigger more 

Andy

[bogstandard]

Darren,

That doesn't look much like a tumbler reverse, maybe a reverse set for cutting left hand threads, tumblers wouldn't have a clamp.

It really does look like you are flogging a dead horse, with too many problems to overcome just to get basic threading sorted.

The simplest way you are going to achieve anything is do what I have to do when screwcutting imperial, some way to reverse the motor. I did that on my Atlas, but it did mean I had to fit a new motor and switch gear to do it. Cost just under 100 squid to buy the bits.

It would most probably be a lot cheaper to source the part you need to make.

You are never going to get this lathe to do everything you really want it to do without throwing your time and cash at it, and even then you still might not get anywhere near to what you really want.

That lathe could have an enthusiastic following, and as it is still in good original condition, you might lose all intrinsic value if you start hacking it about.

It is a bit of a letdown to walk away from a job in defeat, but there is no shame in it.

Maybe this is one of those times.


John

[Darren]

You are possibly quite right John, one of these lathes in worse condition just sold for £160 on the bay without the motor and countershaft. This one is at least compleate, in good condition and running.

The cash could at least be put towards what I would really like and that is a Colchester Student or a Smart and Brown. There is a Smart and Brown up the road from me. Totally unused as he prefers his Viceroy for some reason and the S&B is in the corner with about 8ft of stuff piled on top of it. I have asked about a year ago if he would sell but no was the answer. Maybe I should call again.

The Union has potential with some work but will never be what I really want from a lathe.

I can eliminate the leadscrew backlash quite easily with a little work, but the top slaide will be a little more involved to sort out. Though not impossible.
The motor is reversible and only needs a switch if I could find one.

For the moment though it's all I have and I'm learning something if only what to look for in my next lathe ....  

[Darren]

This would do the reversing

http://cgi.ebay.co.uk/250VAC-DPDT-Centre-OFF-Screw-Terminal-Toggle-Switch_W0QQitemZ170392946135QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item27ac3605d7&_trksid=p3286.c0.m14

[bogstandard]

There is your answer then Darren.

Find your changeover switch and reverse the motor.

The one at the bottom was the one I used and was from Chester UK.


John