Logan 11 spindle adapter

[bcfoster89]

I recently had the need to turn a part between centers (first time for me). I have limited tooling so thought it would be a good opportunity to make a spindle adapter for my Logan 11" lathe. I used 8620 steel, I don't have plans to heat treat and grind it but maybe I could in the future. From my research the spindle taper is 3.75° from center. I used a piece of scrap to make a temporary dead center in the chuck and offset the tailstock to give me the correct taper. I blued the spindle bore and got decent contact from what it looks like, mainly in the middle. I'll hand file and polish until I get a good fit. Then I'll either turn a 60° point on the other end to act as a center (easier) or bore an MT2 hole to use an off the shelf dead center.
Any thoughts on this?

Also, I was running at 270rpm and only taking off .005-.010 doc. It seemed to cut fine but I don't know the limitations of turning between centers? Is there a reduced feed/speed/doc I should be using? Or other safety precautions?

Annoying thing I noticed is that both my temporary dead center in the chuck and live center in the TS were getting chewed up. I'm assuming because of the TS offset causing the centerdrill hole to cut into them. Am I doing something wrong with this?

 

[cathead]

Having read your post, I will give you some of my thoughts, however I do not consider myself an expert on making tapers using the
offset tail stock method. I think it looks pretty good for a first attempt. The first thing I noticed was the little hole in the front of the
tail stock handle which in the past was a repository for lubricant. There is supposed to be a little dauber in that hole to lube the centers.
It seems to me that some machinists used white lead for lube although I have grease in mine. Too much tail stock pressure on the
part might cause noticeable wear on the centers I would think. Your set up offset must be fairly accurate or the bluing would be
concentrated on one end or the other. A lighter cut of just several thousandths might be worth a try if you have plenty of material
to machine on. I have made quite a few Morse tapers using a taper attachment and it is pretty common to have to get out the
file for high spots. I would turn it in the head stock and use a fine mill file, file a little and check the progress and so on. One could
tighten up the gibs some and lock the cross feed for the fine cut and see if that helps any. Sometimes I use a 2x6 inch fine flat
diamond file the long way on the taper while slowly turning it in your hand will allow you to determine if the part really has a high spot
or not.

 

[bcfoster89]

I put some grease on the centers and reduced the TS pressure and that seemed to help with the centers getting eaten up. Unfortunately I hit two more snags!
First one is, after I checked the fit I replaced the part to take another pass and it wasnt running true, I checked my centers with a dial indicator and my TS live center is about .007 out! I'm not sure how to true this up since my chuck is about .010 out and I don't have a four jaw.
My other issue is that I checked the fit after another pass and I get a very odd contact, any thoughts on what might cause this?

 

[twhite]

It could be harmonics. May I suggest a bit larger radius on your cutter slower feed if possible and kick the speed up to 500/600. Then take a few skim passes .002/ side. Before you make first pass give the taper a bit of light sanding. Not much. Just to smooth out. Then use some oil when cutting. Not a bunch just a thin coat on the taper. That might get you closer.

When it is cutting. Be VERY careful and feel if you are getting any vibration. Also you might be having an issue with the drive dog not being secured. It could be floating on and off the stop ever so slightly.


Cutting oil is my blood.

 

[epanzella]

To avoid chewing up centers put a center drilled shaft in a drill chuck and stick a ball bearing between that and your part. It is self aligning to any angle within reason. You can do the same thing at the headstock end.

 

[bcfoster89]

I'll try tightening the cross slide and compound gibs, increasing the speed, and slowing the feed. What should I be very careful doing? This is my first time turning between centers and I definitely don't want anything coming loose. I do think the dog is coming on and off the chuck, especially when I first start since I have to deal with the runout on the TS center making an intermittent cut. It seems to smooth out when its cutting the full diameter.