Dear All,
I am the proud owner of a TDS. I've been fettling bits of it to get the best out of it. One of my problems is a lack of rigidity when turning, and especially when parting.
Now for most small lathes, the convention model-engineering wisdom seems to be that a rear tool-post is the most rigid place for a tool. ...And that would seem to be true for a Myford, where (as I understand it) the saddle gib is a rigid plate bearing on the underside of the rear bed shear. Thus the forces acting on a rear-tool-post-mounted parting tool on a Myford are reacted to by a ground-metal-to-ground-metal bearing between saddle gib and bed.
But for the Viceroy, it seems the saddle is held in place by a Saddle Gib which is designed to be clamped loosely by two cap-screws and spring washers. If it's tightened up, the saddle is semi-locked and the manual says not to do so; if not aggressively tightened, the clamping force on the gib is that of a partially-compressed spring washer. There is a "Saddle Anti-Lifting Clamp" under the bed between the ways, but it bears on surfaces underneath which are not made to be a sliding fit (in fact they are made to have the tailstock clamped to them). So the Anti-Lift Clamp can't be fully tightened either, without jamming the movement of the saddle (and the manual also says not to over-tighten this).
On my lathe, the saddle travels freely, but firm upward hand pressure at the back of the saddle shows it to be able to lift clear of the rear bed-way by perhaps a millimetre. I am not a body-builder, so I am applying perhaps only 20kg force to do this.
Does anyone out there have a view on this please ? :
- have I understood the adjustments ?
- is my lathe as it should be ?
- does this mean that, on a Viceroy, a rear tool post cannot be the aid to rigidity it might be on other lathes ?
dt
TDS 1/1GB saddle and rear tool posts
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
David,
Viceroy lathes have a good reputation for stiffness due to their wide bed, so your post raises a few immediate questions:
1) What are you trying to turn (material and size)
2) Have you checked the headstock bearings for tightness
3) Have you tried different shapes of tool, and honed their cutting faces appropriately?
You don't say what 'fettling' you've done so far. Have you taken the saddle off the bed to check it is clean underneath? Are the cross and top-slide gib strips adjusted? Is there any difference if you lock them up on a test cut?
Dazz had problems getting a decent finish after he rebuilt his TDS - see this thread - might give some pointers. Probably also worth dropping him a PM, to ensure he's aware of this thread.
I believe your adjustments for the saddle retention are correct - my 280VS is set the same, and I've just been facing off an 8" diameter top casting from a rotary table with no hint of vibration. The finish isn't too good yet, but that is down to my tool geometry and finish.
Denford listed a rear tool post as an accessory, (never seen one in use) so I assume they worked fine!
Maybe you can post a few pictures of your setup to help identfiy your problems?
Andy
Viceroy lathes have a good reputation for stiffness due to their wide bed, so your post raises a few immediate questions:
1) What are you trying to turn (material and size)
2) Have you checked the headstock bearings for tightness
3) Have you tried different shapes of tool, and honed their cutting faces appropriately?
You don't say what 'fettling' you've done so far. Have you taken the saddle off the bed to check it is clean underneath? Are the cross and top-slide gib strips adjusted? Is there any difference if you lock them up on a test cut?
Dazz had problems getting a decent finish after he rebuilt his TDS - see this thread - might give some pointers. Probably also worth dropping him a PM, to ensure he's aware of this thread.
I believe your adjustments for the saddle retention are correct - my 280VS is set the same, and I've just been facing off an 8" diameter top casting from a rotary table with no hint of vibration. The finish isn't too good yet, but that is down to my tool geometry and finish.
Denford listed a rear tool post as an accessory, (never seen one in use) so I assume they worked fine!
Maybe you can post a few pictures of your setup to help identfiy your problems?
Andy
Re: TDS 1/1GB saddle and rear tool posts
I am an electronics engineer not mechanical so you may discard this post if it does not make sence. 
I believe most manual lathes use a front toolpost and the spindle direction is ccw so the tool sits upright pushing all the cutting forces downwards (not trying to lift the bed).
With a rear mounted toolpost I would expect the spindle to be running in the CW direction and so again the cutting forces are downwards.
Is this how you have the tools fitted?
On some of the CNC machines the tools cutting from the back are inverted. We are currently redesigning the CNC turret to get downward cutting forces.
I believe most manual lathes use a front toolpost and the spindle direction is ccw so the tool sits upright pushing all the cutting forces downwards (not trying to lift the bed).
With a rear mounted toolpost I would expect the spindle to be running in the CW direction and so again the cutting forces are downwards.
Is this how you have the tools fitted?
On some of the CNC machines the tools cutting from the back are inverted. We are currently redesigning the CNC turret to get downward cutting forces.
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
Steve,
On small manual lathes, the main problem when parting is often a lack of rigidity in the top-slde and tool post. If there is any movement the tendancy is for the tool to be pulled in and down, then it gets to the point where it can't move any more causing it to dig in even harder, generally ending in a 'bang' somewhere!
With a rear toolpost, the work still revolves CCW, but as the toolpost is mounted directly on the cross-slide there is much less transverse movement. If the tool tries to 'bite' now, the tendency will be for it to be lifted out of the cut so decreasing the cut - then it can go back to cutting again. Well, I believe that's the theory, but I've never actually used a rear TP to find out.
BTW - you can't safely run many manual lathes CW under load, as the chuck will simply unscrew iteself! That is partly why the Camlock type chuck fittings were introduced.
The cutting forces/directions involved in parting are quite different to turning a diameter or facing compared to parting-off.
Andy
On small manual lathes, the main problem when parting is often a lack of rigidity in the top-slde and tool post. If there is any movement the tendancy is for the tool to be pulled in and down, then it gets to the point where it can't move any more causing it to dig in even harder, generally ending in a 'bang' somewhere!
With a rear toolpost, the work still revolves CCW, but as the toolpost is mounted directly on the cross-slide there is much less transverse movement. If the tool tries to 'bite' now, the tendency will be for it to be lifted out of the cut so decreasing the cut - then it can go back to cutting again. Well, I believe that's the theory, but I've never actually used a rear TP to find out.
BTW - you can't safely run many manual lathes CW under load, as the chuck will simply unscrew iteself! That is partly why the Camlock type chuck fittings were introduced.
The cutting forces/directions involved in parting are quite different to turning a diameter or facing compared to parting-off.
Andy
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davidsbthomas
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Re: TDS 1/1GB saddle and rear tool posts
Yes, Andy describes my problem better than I did. It is largely to do with parting. I've experienced bad finish in plain turning, but it usually turns out to be my own poor tool-grinding at fault.
The conventional wisdom I referred to in my original post is that if you fit a rear toolpost and an inverted parting tool, maintaining the usual direction of rotation, you get a more rigid set-up (because, amongst other things, the rear toolpost is no longer on top of a transversely mounted topslide) and a kinder mode of failure (because if the cut fails, the tool gets pushed away instead of being 'sucked-in').
To answer your questions Andy, I'm confident that my headstock is OK; my fettling has included careful cleaning, lubricating and adjusting of cross-slide and top-slide, both of which were wobbly because poorly set.
I have a very confidence-inspiring rigid Multifix toolpost, and a great big stiff and carefully ground parting tool. My TDS is 3-phase and driven through an inverter, so I can use more or less any speed. But I still can't part reliably, and so I turned my attention to checking the saddle and thinking about a possible rear tool post.
What worries me is that a saddle which is only loosely attached to the machine makes the kind of dig-in you describe almost inevitable with a front tool-post, and at the same time undermines a solution based on a rear tool post.
dt
The conventional wisdom I referred to in my original post is that if you fit a rear toolpost and an inverted parting tool, maintaining the usual direction of rotation, you get a more rigid set-up (because, amongst other things, the rear toolpost is no longer on top of a transversely mounted topslide) and a kinder mode of failure (because if the cut fails, the tool gets pushed away instead of being 'sucked-in').
To answer your questions Andy, I'm confident that my headstock is OK; my fettling has included careful cleaning, lubricating and adjusting of cross-slide and top-slide, both of which were wobbly because poorly set.
I have a very confidence-inspiring rigid Multifix toolpost, and a great big stiff and carefully ground parting tool. My TDS is 3-phase and driven through an inverter, so I can use more or less any speed. But I still can't part reliably, and so I turned my attention to checking the saddle and thinking about a possible rear tool post.
What worries me is that a saddle which is only loosely attached to the machine makes the kind of dig-in you describe almost inevitable with a front tool-post, and at the same time undermines a solution based on a rear tool post.
dt
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davidsbthomas
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Re: TDS 1/1GB saddle and rear tool posts -- progress
Just to report a discovery and some progress.
I took my saddle off. I discovered that the stud which holds the Saddle Anti-Lift Clamp to the underside was unsatisfactory in several ways:
- the clamp-plate is held on to it by a Nyloc nut, which somebody in the past had loosened (perhaps to remove the saddle ?). But the grip of the Nyloc was too great, and instead of undoing the nut, the stud had come loosely unscrewed
- coupled with the fact that the plate has a large hole and a very loose fit on the stud, this meant that the plate tended to swivel and/or tilt, and jam against the underside of the bed even though it was actually not tight enough (rather than too tight) against the underside
- the plate was burred and scored where it should ride on the underside of the bed (perhaps it got swarf in the gap?)
So I cleaned up the stud and Loctited it into the hole with a substantial locknut against the underside of the saddle for good measure. I cleaned up and lightly filed the sliding surfaces of the clamp plate. I refitted the clamp plate with a compression spring on the stud, pressing the plate down onto the Nyloc nut (and washer). Thus any tendency for the plate to flop about and jam has been controlled.
The result is I can now tighten the Saddle Anti-Lift Clamp to the point where it JUST doesn't interfere with saddle movement.
I also cleaned up both the saddle gib at the rear, and the bed shear it runs on, with a scotchbrite pad, removing some ancient grease deposits etc. I then regreased them and reassembled, but this treatment seems to allow me to tighten the rear gib more effectively without jamming the saddle. I'm not sure to what extent this and the improvements to the saddle clamp are helping each other.
The overall net effect is that the saddle no longer lifts at the rear with hand pressure. Because the saddle clamp is on the right-hand side of the saddle, the improvement is not quite symmetrical. I really can't feel the right wing of the saddle lift, but in a bright light I can see that tugging on the left wing disturbs the oil film underneath it. However, that suggests movement in the order of small fractions of a millimetre rather than the gross klunking I had before.
The discovery is, therefore, that although the TDS saddle design is a bit crude, it can be made to behave quite well with a little care. Next step: go back to thinking about a rear toolpost.
I took my saddle off. I discovered that the stud which holds the Saddle Anti-Lift Clamp to the underside was unsatisfactory in several ways:
- the clamp-plate is held on to it by a Nyloc nut, which somebody in the past had loosened (perhaps to remove the saddle ?). But the grip of the Nyloc was too great, and instead of undoing the nut, the stud had come loosely unscrewed
- coupled with the fact that the plate has a large hole and a very loose fit on the stud, this meant that the plate tended to swivel and/or tilt, and jam against the underside of the bed even though it was actually not tight enough (rather than too tight) against the underside
- the plate was burred and scored where it should ride on the underside of the bed (perhaps it got swarf in the gap?)
So I cleaned up the stud and Loctited it into the hole with a substantial locknut against the underside of the saddle for good measure. I cleaned up and lightly filed the sliding surfaces of the clamp plate. I refitted the clamp plate with a compression spring on the stud, pressing the plate down onto the Nyloc nut (and washer). Thus any tendency for the plate to flop about and jam has been controlled.
The result is I can now tighten the Saddle Anti-Lift Clamp to the point where it JUST doesn't interfere with saddle movement.
I also cleaned up both the saddle gib at the rear, and the bed shear it runs on, with a scotchbrite pad, removing some ancient grease deposits etc. I then regreased them and reassembled, but this treatment seems to allow me to tighten the rear gib more effectively without jamming the saddle. I'm not sure to what extent this and the improvements to the saddle clamp are helping each other.
The overall net effect is that the saddle no longer lifts at the rear with hand pressure. Because the saddle clamp is on the right-hand side of the saddle, the improvement is not quite symmetrical. I really can't feel the right wing of the saddle lift, but in a bright light I can see that tugging on the left wing disturbs the oil film underneath it. However, that suggests movement in the order of small fractions of a millimetre rather than the gross klunking I had before.
The discovery is, therefore, that although the TDS saddle design is a bit crude, it can be made to behave quite well with a little care. Next step: go back to thinking about a rear toolpost.
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
Glad to hear you've removed some rattle.
I've just been re-reading the section on parting in George Thomas' "The Model Engineers Workshop Manual".
It begs a few more questions about where your parting goes wrong - right from the initial cut or once you are part way through?
The latter is often caused by swarf jamming in the groove, and can be eased by grinding the front of the tool to a 'V' (10-20 deg angle each side).
He also suggests that many people try to part off too slowly (200-300 rpm for 1" steel bar).
You are clamping the saddle when parting I assume?
And blade set just below centre height for a front mounted tool.
I really must get round to making my parting tool holder fit my toolpost, then I can try all this for myself!!
Why grease? I would have thought you'd have grinding paste in there in no time as bits of swarf get stuck to the grease. Slideway oil would be much more suitable, IMHO.davidsbthomas wrote: I also cleaned up both the saddle gib at the rear, and the bed shear it runs on, with a scotchbrite pad, removing some ancient grease deposits etc. I then regreased them and reassembled
I've just been re-reading the section on parting in George Thomas' "The Model Engineers Workshop Manual".
It begs a few more questions about where your parting goes wrong - right from the initial cut or once you are part way through?
The latter is often caused by swarf jamming in the groove, and can be eased by grinding the front of the tool to a 'V' (10-20 deg angle each side).
He also suggests that many people try to part off too slowly (200-300 rpm for 1" steel bar).
You are clamping the saddle when parting I assume?
And blade set just below centre height for a front mounted tool.
I really must get round to making my parting tool holder fit my toolpost, then I can try all this for myself!!
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davidsbthomas
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Re: TDS 1/1GB saddle and rear tool posts
You make a good point about the grease.
But from the goo I removed, grease had obviously been used before, and no 'grinding paste' effect was apparent. The original surface scraping marks on the rear gib plate are still there (and the lathe is about 35 years old).
I used a soft CL grease - just a smear - it's more like Non-Drip Oil than bearing grease. I expect it will get dissolved anyway in due course by slideway oil making its way round from above.
But from the goo I removed, grease had obviously been used before, and no 'grinding paste' effect was apparent. The original surface scraping marks on the rear gib plate are still there (and the lathe is about 35 years old).
I used a soft CL grease - just a smear - it's more like Non-Drip Oil than bearing grease. I expect it will get dissolved anyway in due course by slideway oil making its way round from above.
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
Had another thought this morning - is your chuck holding the stock tightly?
I used a Colchester Bantam a few years ago, and had terrible problems getting a good finish whilst parting led to a few broken tools. On closer inspection, the jaws on the 3-jaw chuck were so worn as to be 'bell-mouthed'. After that I used the 4-jaw which had seen very lttle use, and everything was much easier!
So if you have an old chuck, have you dismantled it and given it a good clean out?
I used a Colchester Bantam a few years ago, and had terrible problems getting a good finish whilst parting led to a few broken tools. On closer inspection, the jaws on the 3-jaw chuck were so worn as to be 'bell-mouthed'. After that I used the 4-jaw which had seen very lttle use, and everything was much easier!
So if you have an old chuck, have you dismantled it and given it a good clean out?
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
Here is the drawing for the Denford rear tool post machined casting.
I don't have a copy of the assembly drawing, ML117.
Admin may be able to find it.
I don't have a copy of the assembly drawing, ML117.
Admin may be able to find it.
- Attachments
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- Rear tool post machined casting for Denford 5" lathe
- ML117-1#.jpg (126.27 KiB) Viewed 16470 times
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Denford Admin
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Re: TDS 1/1GB saddle and rear tool posts
Had a quick look and can't find any ML117's (even the one you've posted)
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davidsbthomas
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Re: TDS 1/1GB saddle and rear tool posts
Thanks Andy for the drawing.
I haven't been back to the lathe yet to test my new set up in parting.
But from the much improved feel of the saddle motion, I'm confident my major problem was the wobbly and maladjusted clamp and gib. It really can't help rigity to have a saddle which is only vaguely associated with the rest of the machine.
As to the chuck, I think it's fine. Besides, I have a 4-jaw as well as a 3-jaw, so they can't both be bust.
I haven't been back to the lathe yet to test my new set up in parting.
But from the much improved feel of the saddle motion, I'm confident my major problem was the wobbly and maladjusted clamp and gib. It really can't help rigity to have a saddle which is only vaguely associated with the rest of the machine.
As to the chuck, I think it's fine. Besides, I have a 4-jaw as well as a 3-jaw, so they can't both be bust.
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molyneux.mike
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Re: TDS 1/1GB saddle and rear tool posts
Dear All
I was looking at this old post about Rear Tool Posts and saw the drawings which will allow me to fabricate one.
Does anyone know how the Rear Tool Post fits onto the Lathe? A drawing, sketch, template or explanation would help.
Thanks
I was looking at this old post about Rear Tool Posts and saw the drawings which will allow me to fabricate one.
Does anyone know how the Rear Tool Post fits onto the Lathe? A drawing, sketch, template or explanation would help.
Thanks
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Andy B
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Re: TDS 1/1GB saddle and rear tool posts
Hi Mike,
I believe they fitted onto the T-slotted cross-slide, which was an optional extra on the 5" machines.
They may fit on a 280's too, but I don't recall seeing one in any 280 brochure.
Andy
I believe they fitted onto the T-slotted cross-slide, which was an optional extra on the 5" machines.
They may fit on a 280's too, but I don't recall seeing one in any 280 brochure.
Andy
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molyneux.mike
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Re: TDS 1/1GB saddle and rear tool posts
Hi Andy
The T-slotted cross-slide explains it.
I will see if it feasible to make some sort of adaptor plate to allow the mounting of the tool post on the existing cross-slide.
Thanks for info.
Mike
The T-slotted cross-slide explains it.
I will see if it feasible to make some sort of adaptor plate to allow the mounting of the tool post on the existing cross-slide.
Thanks for info.
Mike
Re: TDS 1/1GB saddle and rear tool posts
Hello All
I am a newomer to the forum and like David I purchased a TDS mk 2 at auction and was having trouble with rigidity. After reading the comments on this site I moved the saddle over the end of the bed so I could get a better look at the lift clamp and it was also slack and clogged up with swarf and wood dust. I also found that the caphead screw on the leadscrew bracket was loose which would have explained why I was having difficulty screw cutting. After a good clean and tighten up the lathe now has a much more postive feel.
My lathe came with no accessories apart from a 3 jaw chuck and a catch plate. I got fixed up with an excellent thread indicator thanks to Mike Molyneux whom I contacted from this site.
I was adjusting the topslide when I found that the grubscrews had been ground to long fine point,surely this not correct? I see in the manual that these are listed as 2BAx7/8" nylon insert grubs,are they special screws or is there a separate nylon insert?
You don't happen to have a drawing of a saddle stop at Admin? I would appreciate if you could find one.
Cheers Ivan
I am a newomer to the forum and like David I purchased a TDS mk 2 at auction and was having trouble with rigidity. After reading the comments on this site I moved the saddle over the end of the bed so I could get a better look at the lift clamp and it was also slack and clogged up with swarf and wood dust. I also found that the caphead screw on the leadscrew bracket was loose which would have explained why I was having difficulty screw cutting. After a good clean and tighten up the lathe now has a much more postive feel.
My lathe came with no accessories apart from a 3 jaw chuck and a catch plate. I got fixed up with an excellent thread indicator thanks to Mike Molyneux whom I contacted from this site.
I was adjusting the topslide when I found that the grubscrews had been ground to long fine point,surely this not correct? I see in the manual that these are listed as 2BAx7/8" nylon insert grubs,are they special screws or is there a separate nylon insert?
You don't happen to have a drawing of a saddle stop at Admin? I would appreciate if you could find one.
Cheers Ivan
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Re: TDS 1/1GB saddle and rear tool posts
Can you tell me a drawing number ?You don't happen to have a drawing of a saddle stop at Admin? I would appreciate if you could find one.
Re: TDS 1/1GB saddle and rear tool posts
Sorry I have no drawing number.
Thankyou for prompt reply.
Regards Ivan
Thankyou for prompt reply.
Regards Ivan
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Re: TDS 1/1GB saddle and rear tool posts
Have a look at the top of the Viceroy section - I've scanned a load of drawings that might show what you're after
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dazz
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Re: TDS 1/1GB saddle and rear tool posts
Hi
I know this is an old thread but....
I found that improved tool grinding was only part of the solution.
Watching this video shows how sharp tools cause rubbish finish.
http://www.youtube.com/watch?v=mRuSYQ5Npek
What is happening is that a built up edge (BUE) is forming on the tool edge then breaking off causing what looks like a torn and rough finish.
The BUE welds onto the edge and gets bigger until it breaks off.
The solution is to either increase or decrease cutting speed to get out of the BUE range. Other factors such as coolant can help reduce BUE.
When I use carbide tooling I set the speed to scary fast and the DoC/ feed to smoking-drive-belt.
The rear toolpost takes advantage of flex. As the tool pressure increases, the tool is pulled up and away from the workpiece. This negative feedback stabilises the cutting action.
On the front tool post, when the tool pressure increases, the tool flexes down and dives forward into the workpiece. This positive feedback makes the cutting action unstable.
I know this is an old thread but....
I found that improved tool grinding was only part of the solution.
Watching this video shows how sharp tools cause rubbish finish.
http://www.youtube.com/watch?v=mRuSYQ5Npek
What is happening is that a built up edge (BUE) is forming on the tool edge then breaking off causing what looks like a torn and rough finish.
The BUE welds onto the edge and gets bigger until it breaks off.
The solution is to either increase or decrease cutting speed to get out of the BUE range. Other factors such as coolant can help reduce BUE.
When I use carbide tooling I set the speed to scary fast and the DoC/ feed to smoking-drive-belt.
The rear toolpost takes advantage of flex. As the tool pressure increases, the tool is pulled up and away from the workpiece. This negative feedback stabilises the cutting action.
On the front tool post, when the tool pressure increases, the tool flexes down and dives forward into the workpiece. This positive feedback makes the cutting action unstable.
Last edited by dazz on Thu 16 Aug , 2012 9:21 am, edited 1 time in total.
Regards
Dazz
Dazz