Shiny bands on work

[Richard1]

I'm getting shiny bands on work when I am turning under power feed on a Myford Super 7. The bands are I guess about 20 thou wide and at regular 1/8 inch spacing. They are cut into the work by an amount unmeasurable with my equipment but are the last things to vanish when I lap the OD.

Because the spacing is 1/8 inch and the Myford leadscrew is 8 TPI I think they are related and am guessing a bent leadscrew but would welcome all suggestions on other possible causes and cure.

The reason I suspect a bent lead screw is because the lathe was stolen a while ago by Peter Underhay a burglar so amazingly incompetent that when I recovered it he had set the motor on fire, destroyed the Dewhurst switch and bent both the front bracket on the cross slide and the cross feed screw, the Allen screws holding the front bracket on the cross slide were slacked off 2 turns so the cross feed screw could be turned at all.

Richard

 

[bearcar1]

"Steal a man's beer but don't steal his tools" is an old adage we used to quote at work. I cannot help answer your question regarding the banding but does it occur on all metals being turned such as brass and aluminum as well as steel? If yes than there is something amiss somewhere as it is too repetitive to merely be hard spots or the occasional piece of swarf under the cutter. A bent lead screw? How in bloody hell could he have accomplished that? How did he move such a chunk of metal as a M& anyway?


BC1
Jim

 

[GailInNM]

Richard,
I had a Nardini some years back that did the same thing new from the factory. It had a square drive feed separate from the lead screw that was warped, but the same thing would happen if the lead screw and feed were combined as I think the Myford is. My feed drive was just mild steel, so it was easy enough to straighten in place. Well, not really easy, but possible.

You should be able to put a piece of flat sheet metal or ground stock across several thread of the leadscrew and indicate the leadscrew with a dial indicator on the sheet metal to see if this is the problem. If it is, you may be able to straighten the lead screw with a improvised screw jack between the lead screw and the bench. If it was soft enough to bend once, it should be soft enough to bend back.

If the Myford uses a key drive for the power feed it may be that the key is a little bit thick and lifting the carriage. If so, grinding a few thou off the key might help.

Gail in NM

 

[Richard1]

"Steal a man's beer but don't steal his tools" is an old adage we used to quote at work. I cannot help answer your question regarding the banding but does it occur on all metals being turned such as brass and aluminum as well as steel? If yes than there is something amiss somewhere as it is too repetitive to merely be hard spots or the occasional piece of swarf under the cutter. A bent lead screw? How in bloody hell could he have accomplished that? How did he move such a chunk of metal as a M& anyway?

I'm not sure if it occurs on all metals as I hardly ever turn anything but 316 stainless on it but I think I recall seeing it on a bit of brass weeks ago. I shall experiment this week with different materials and sizes to see what happens. I am guessing that he dropped it on the floor and most of the weight went on the leadscrew handwheel bending the end of the screw. I can't imagine how he managed to bend the cross feed screw or the bracket on the cross slide but I had to machine a 3 degree angle on the bolting face before I could put it back together.

 

[Richard1]

Gail,

good idea I will try indicating it in several places along the length of it and will check the key, if it is lifting the saddle a little that would certainly explain it. Not sure how it could be but has to be worth a look. Will also put the gear box in neutral and feed with the leadscrew handwheel to verify it is not something in the gearbox giving a bump every revolution.

Richard.

 

[pete]

Richard,
If you have house hold theft insurance on your tools I'd contact your insurance agent immediately and tell him you expect your lathe to be sent to Myford to be returned to the original condition it was before the theft.

Pete