New member - help please

Good afternoon all,

I am a new member so please bear with me if I sound a bit dumb. I have recently bought an elderly Colchester Master metal working lathe. I had one years ago and decided something was missing in my workshop.

She was built in 1940, so she has worked hard during her life. Turning along the bed she works really well. I decided to check the cross slide by truing up the face plate. Working from the centre she cuts nicely but as she get to about halfway to the outer edge she cuts less and less until she is hardly touching the face plate.

Any suggestions please as to the solution. Is there something I can adjust or is something bent?

Thanks in advance.

Tonytilly said:

Good afternoon all,

I am a new member so please bear with me if I sound a bit dumb. I have recently bought an elderly Colchester Master metal working lathe. I had one years ago and decided something was missing in my workshop.

She was built in 1940, so she has worked hard during her life. Turning along the bed she works really well. I decided to check the cross slide by truing up the face plate. Working from the centre she cuts nicely but as she get to about halfway to the outer edge she cuts less and less until she is hardly touching the face plate.

Any suggestions please as to the solution. Is there something I can adjust or is something bent?

Thanks in advance.

Click to expand...

More likely something worn. Normally a lathe is set up so it cuts just a tiny bit deeper so there is a barely noticeable concavity to faced parts. In your case it sounds as if the cross slide had more wear closer to the center from turning small parts.

Since you are experienced I did not suggest what I might to a newbie that the tool bit may not be on center and is being pushed away by rubbing.

You could well be right about being used for small parts Scottl. I had not thought of that. For the age of her, I can't expect miracles but I would like to try and get things as they should be. I will take the cross slide off and have a look see.

Thanks very much for taking the trouble of replying. Tony.

Okay, .what tool material are you using? HSS grade or name it can vary from crap to really good, or brazed TC again brand etc, ......or TC insert name shape grade etc etc it all makes a difference.

What RPM and feed are you using?

At about what dia are you failing to touch the face plate?

Tonytilly,

(Site owner likes searchable titles on posts, such as "Facing trouble on Colchester Master lathe")

Not yet mentioned, is the saddle locked down to the bed when facing??? Absolutely necessary on my old South Bend, not so much on a LeBlond Servo Shift I used at the local community college...

John

I am using HSS, as for grade it is a Myford tool from my old ML7. RPM not sure, she is an old lathe with a minimum information available. The cutting starts to reduce about 3" from the centre.

Point taken with regard to searchable title comstockfriend, it's noted.

I do have a problem with the saddle lock. I will double check that it is working correctly. That is a very good point, thank you.

TonyTilly,

If you hurry, click on "Edit Post" and then scroll down to "Go Advanced" and edit your title block. You must act quickly, because the "Edit Post" button goes away at some interval after the post.

I write this in a spirit of helpfulness, because the forum rules state that a meaningful, searchable title is MANDATORY.

Which direction are you feeding on that facing cut ? If you grind your toolbit so it cuts on the "pull out" direction, you may find there is less tendency for the work to be convexed or "coned". A faceplate is a larger diameter, and as your tool moves across it during a facing cut, the cutting speed (also known as "rim speed" or "surface speed") changes continuously. In other words, out at the rim or outer circumference of the faceplate, if you calculated the rim speed or cutting speed, you would get a relatively high speed. If you picked a diameter of the faceplate near the spindle, you would find at that same rpm, the surface speed is quite a bit lower. If you feed the toolbit at the same rate, the chip load on the tool increases as you get into that smaller diameter region, and it puts quite a bit more load on the tool- and the tendency is to push it away from the work. I'd suggest you grind a sharp facing toolbit, such that the cutting edge will cut on the "pull out" direction. Run your lathe at an rpm that is about the average of the rpm required at the innermost and outermost diameters of the faceplate.
Cutting speed for cast iron with a high speed steel toolbit is about 60-80 ft/min in good clean cast iron. I know you are in France, so you are likely thinking in metric units. I am old school here in the USA, and my mind thinks in "Imperial" (inch, feet, pounds, etc) units, so please bear with me. Basically, if you took the diameter of your faceplate at the rim and multiplied it by 2 x Pi (3.14159), you would have the circumference. The cutting speed (which may be in meters per second) x 60 seconds per minute = cutting speed in Meters/minute. Divide this by the circumference of the faceplate (or location on it) and you have the rpm required at that location on the faceplate. Since you can't vary the speed of your lathe spindle as your tool traverses the faceplate, I would take an average. Feed the tool from the spindle area pulling out, and take a very light cut. At the spindle area, you feed slowly, and as you pull out, you can increase the rate at which you are cranking the tool outwards. By taking very light cuts and pulling out, as well as making sure the carriage is locked solidly to the bed, I think you may find the problem is greatly reduced, if not eliminated.

Tonytilly said:

I am using HSS, as for grade it is a Myford tool from my old ML7. RPM not sure, she is an old lathe with a minimum information available. The cutting starts to reduce about 3" from the centre.

Click to expand...

Rock bottom speed, - should be around 25RPM IIRC, a good 1/16'' rad min on the tool, and not too fine a feed say <> 0.005 '' / rev MINIMUM or the tooltip will wear too much before you get to the OD.

Go here http://www.lathes.co.uk/colchestermasterearly/ and if it's the same machine I did remember correctly - 4th pic down

Colchester Master cutting out of true

Sorry SouthBendModel34, I can't find the Edit Post button.

Problem solved!

Thanks to everyone for their advice. I removed the saddle from the lathe to double check the saddle lock. The was no or ever has been a saddle lock on this lathe. Quite bizarre. I have never come across this before. Perhaps this is something to do with war time manufacture and cost cutting. I therefore drilled and tapped a hole in a suitable place on the saddle, installed a bolt. Reinstalled the saddle, reground the tool tip, reset the speed to 44 rpm, locked the saddle and she cut a beautiful flat face plate.

So there we are... problem solved. Thanks again to everyone for their input. Kind regards, Tony

I only EVER use a carbide bit and SLOW RPM when facing off a large object,such as taking a truing cut on the faceplate of a new lathe. If you're feeding towards the center,with a HSS bit,your problem may be that the cutting edge of the HSS bit is getting completely worn away till it is not touching the cast iron.

You may have already solved this problem. I don't feel up to reading all the posts this A.M. as I've got a headache. But,if you haven't solved it,use a carbide bit,and run the lathe at the slowest speed possible.

The trouble with most lathes is they won't run SLOW enough. Especially the newer ones,and the smaller ones,as in your case. I had a large lathe at work that would run 11 rpm. It took a long time to face off the face plate,but it did work. And,that face plate as at least 16" in diameter. Very high peripheral speed.I did not want to ever stop the lathe to speed it up as it got closer to the center of the face plate,as the cuts would look different. So,just had to wait,but got a nice,clean,even looking cut. Time spent was not an issue as I had plenty of "slack time" being the tool maker in a museum!

Limy Sami said:

Rock bottom speed, - should be around 25RPM IIRC, a good 1/16'' rad min on the tool, and not too fine a feed say <> 0.005 '' / rev MINIMUM or the tooltip will wear too much before you get to the OD.

Go here http://www.lathes.co.uk/colchestermasterearly/ and if it's the same machine I did remember correctly - 4th pic down

Click to expand...

Spot on Limy Sami. Believe it or not my model lathe is the one before that! Mine was built in 1940 the one in your photo link must be just post war.