Mn80 Lathe - Saddle travel problem

[Ttrevor]

Hello,
I have a small TOS Mn80 Lathe. I bought it second hand in 1996 with my redundancy payment, I have not used it very much. I noticed a strange sound that rises in pitch when the saddle was moved towards the tailstock end. The sound is a bit like running your thumb along the teeth of a comb and it rises in pitch as it goes, and the saddle also gets tight on aproaching the far right end especially if the saddle can travel further after removing the tail stock. The saddle is very tight at the end until I move it back to the left and the sound decreases in pitch as the saddle moves back to the left, like a Piano ! If I turn the Lead screw slightly and repeat the travel along the bed, the sound changes, at 180 degree rotration of the Lead screw, there is no sound until the saddle gets near the tailstock end, also, If I Oil the lead screw threads, this also reduces the tightness and noise. so I think it may be Half Nuts not clearing the lead screw, I can understand that this may make the noise but not the tightness. There is no diagram in handbook. .
Initially, I thought it was the gear on the rack causing the noise and tightness as that's what I was turning, but the gear on the rack has slight and even play even when the saddle goes tight so I don't think it is. Only recently did I discover the Lead screw may be the culprit. I would like to know how to disassemble the apron ( and if possibly get it back together ! ), there is no maintenance manual for this lathe as far as I know, I only have a general user manual and diagrams showing setup tolerances when the machine was new.
Does anyone have any sugestions on what could cause this problem and what may be the cure. I did not want to pull it to bits and loose all the setup tolerances as it is working ok at the headstock end, but I don't like it when I know something is amiss. I would rather watch someone who knows what they are doing, and learn.
Trevor

 

[Richard King]

I suspect the machine is worn in the middle. Take a micrometer and measure the box ways every 4" - 101.6 mm front and back side. On most lathes the underside of the box ways are original and it only wears on top. Also take some spray or brush on layout bluing on the feed screw and move the saddle to the left and right. If the saddle is worn it may drag on the feed screw. To see if the saddle is low for a test, loosen the saddle screws that hold it to the cariaige and see if it gets loose. I'm not familiar with the lathe accept all lathes work the same. Have you loosened the saddle lock? Does the back strap under the saddle have a gib that someone may have tightened? Be a detective and figure it out. Here is some info and pictures of the lathe

TOS MN80 & SU16 Lathes

 

[Ralph_P]

The lead screw could be bent. It can be straitened. The lead screw support on the tailstock end may need adjustment, up or down.

 

[Ttrevor]

Hi Richard,

Thank you very much for replying.
I shall do what you suggest as soon as I can. I need to plan exactly how to do these tests and set aside plenty of time. I was wondering about trying to test the lathe for accuracy as I have documents that came with the lathe showing all the tolerances. (see below), even though I scanned them all the same page b was too large so I cropped it and resent it. Problem is I never got around to translating.
Feed screw
By the Feed Screw, are you refering to the Lead screw.?
Saddle lock
The saddle lock is loose, it is a very good lock when turned it locks the saddle very tightly and it can not be moved at all.
Gib strip
I don't know if there is a gib, I am not sure where to look will there be one at the front and one at the back.I shall have to investigate that, I have not touched any of the fasteners they are just as they were in 1996
Link to Mn80 and SU16, I had already seen that site but nice of you go searching for me. I appreciate that thank you.

I will see what I can do tomorrow if I have time and get back to you.

Regards
Trevor.

I suspect the machine is worn in the middle. Take a micrometer and measure the box ways every 4" - 101.6 mm front and back side. On most lathes the underside of the box ways are original and it only wears on top. Also take some spray or brush on layout bluing on the feed screw and move the saddle to the left and right. If the saddle is worn it may drag on the feed screw. To see if the saddle is low for a test, loosen the saddle screws that hold it to the cariaige and see if it gets loose. I'm not familiar with the lathe accept all lathes work the same. Have you loosened the saddle lock? Does the back strap under the saddle have a gib that someone may have tightened? Be a detective and figure it out. Here is some info and pictures of the lathe

TOS MN80 & SU16 Lathes

 

[Ttrevor]

The lead screw could be bent. It can be straitened. The lead screw support on the tailstock end may need adjustment, up or down.

Hi Ralph,
Thank you very much for replying.
I too was wondering if the Lead screw might be bent, but not sure how that could have happened. The lathe was delivered together with a Harrison Jubilee wood lathe in the back of a rusty old pickup all the way from London to Lancaster, not even tied down with just a taupaulin. so whether it may have recieved a knock i will never know but this Lead screw problem was already present when I received it. I don't think the lathe has had very much use. The Lead screw is 16mm diameter and 3mm pitch.
Leadscrew ajustment
The bush is secured by two bolts and there is also a oil point that I did not know about so a put some oil in that for the first time. (oops) I will have a look tomorrow, it difficult to tell if there is any ajustment as the joint is all painted green, I would have to chip off the paint which seems a shame. I shall look tomorrow and take a picture or two.

Regards
Trevor

 

[Ttrevor]

Hi Richard,

Thank you very much for replying.
I shall do what you suggest as soon as I can. I need to plan exactly how to do these tests and set aside plenty of time. I was wondering about trying to test the lathe for accuracy as I have documents that came with the lathe showing all the tolerances. (see below)
Feed screw
By the Feed Screw, are you refering to the Lead screw.?
Saddle lock
The saddle lock is loose, it is a very good lock when turned it locks the saddle very tightly and it can not be moved at all.
Gib strip
I don't know if there is a gib, I am not sure where to look will there be one at the front and one at the back.I shall have to investigate that, I have not touched any of the fasteners they are just as they were in 1996
Link to Mn80 and SU16, I had already seen that site but nice of you go searching for me. I appreciate that thank you.

I will see what I can do tomorrow if I have time and get back to you.

Regards
Trevor.

I suspect the machine is worn in the middle. Take a micrometer and measure the box ways every 4" - 101.6 mm front and back side. On most lathes the underside of the box ways are original and it only wears on top. Also take some spray or brush on layout bluing on the feed screw and move the saddle to the left and right. If the saddle is worn it may drag on the feed screw. To see if the saddle is low for a test, loosen the saddle screws that hold it to the cariaige and see if it gets loose. I'm not familiar with the lathe accept all lathes work the same. Have you loosened the saddle lock? Does the back strap under the saddle have a gib that someone may have tightened? Be a detective and figure it out. Here is some info and pictures of the lathe

The lead screw could be bent. It can be straitened. The lead screw support on the tailstock end may need adjustment, up or down.

Hi again,

I have just been looking at the online pictures on the site that Richard sent the Link to, and there is something odd on the first picture. There are two large black objects on the Lead screw that are not in any other of the pictures. What do you think these are ?
Regards
Trevor

 

[Ttrevor]

Hi Ralph,
Thank you very much for replying.
I too was wondering if the Lead screw might be bent, but not sure how that could have happened. The lathe was delivered together with a Harrison Jubilee wood lathe in the back of a rusty old pickup all the way from London to Lancaster, not even tied down with just a taupaulin. so whether it may have recieved a knock i will never know but this Lead screw problem was already present when I received it. I don't think the lathe has had very much use. The Lead screw is 16mm diameter and 3mm pitch.
Leadscrew ajustment
The bush is secured by two bolts and there is also a oil point that I did not know about so a put some oil in that for the first time. (oops) I will have a look tomorrow, it difficult to tell if there is any ajustment as the joint is all painted green, I would have to chip off the paint which seems a shame. I shall look tomorrow and take a picture or two.

Regards
Trevor

I have just been looking at the online pictures on the site that you sent the Link to, and there is something odd on the first picture. There are two large black objects on the Lead screw that are not in any other of the pictures. What do you think these are ?
Regards
Trevor

 

[Ttrevor]

Hi Richard,

Thank you very much for replying.
I shall do what you suggest as soon as I can. I need to plan exactly how to do these tests and set aside plenty of time. I was wondering about trying to test the lathe for accuracy as I have documents that came with the lathe showing all the tolerances. (see below)
Feed screw
By the Feed Screw, are you refering to the Lead screw.?
Saddle lock
The saddle lock is loose, it is a very good lock when turned it locks the saddle very tightly and it can not be moved at all.
Gib strip
I don't know if there is a gib, I am not sure where to look will there be one at the front and one at the back.I shall have to investigate that, I have not touched any of the fasteners they are just as they were in 1996
Link to Mn80 and SU16, I had already seen that site but nice of you go searching for me. I appreciate that thank you.

I will see what I can do tomorrow if I have time and get back to you.

Regards
Trevor.


I have just been looking at the online pictures on the site that Richard sent the Link to, and there is something odd on the first picture. There are two large black objects on the Lead screw that are not in any other of the pictures. What do you think these are ?
Regards
Trevor

Doughh. they are the knobs on the steadies Sorry.

 

[Ttrevor]

Hi Richard,

Thank you very much for replying.
I shall do what you suggest as soon as I can. I need to plan exactly how to do these tests and set aside plenty of time. I was wondering about trying to test the lathe for accuracy as I have documents that came with the lathe showing all the tolerances. (see below)
Feed screw
By the Feed Screw, are you refering to the Lead screw.?
Saddle lock
The saddle lock is loose, it is a very good lock when turned it locks the saddle very tightly and it can not be moved at all.
Gib strip
I don't know if there is a gib, I am not sure where to look will there be one at the front and one at the back.I shall have to investigate that, I have not touched any of the fasteners they are just as they were in 1996
Link to Mn80 and SU16, I had already seen that site but nice of you go searching for me. I appreciate that thank you.

I will see what I can do tomorrow if I have time and get back to you.

Regards
Trevor.


I have just been looking at the online pictures on the site that Richard sent the Link to, and there is something odd on the first picture. There are two large black objects on the Lead screw that are not in any other of the pictures. What do you think these are ?
Regards
Trevor

Doughh. they are the knobs on the steadies Sorry.

 

[Richard King]

Yes feed is same as lead screw...on the saddle feed. One of those pictures from UL it looks like there may be a tapered gib under the saddle in the front. It may have been adjusted in the middle of the wear area...middle.. If it has one, loosen it a little. Your welcome. I like to help and play detective :-)