[How do I?] Mill The Round Slot For My Replacement Cross-feed Slide?

[Rex Walters]

I'm attempting to replace (upgrade) the cross-feed slide on my old Logan lathe with the very nice iron casting I purchased from Andy Lofquist at Metal Lathe Accessories. I've been really wanting a "boring table" like George Thomas describes in his books and are apparently the norm with Myford lathes. The casting is really made for a South Bend lathe (see details at the practical machinist thread) which uses a different design for attaching the compound slide, but the overall dimensions still work quite nicely for my Logan (Wards) lathe. Here's a model I made of the original Logan slide:



I'm kinda stumped on how to mill the circular slot. I can't use a normal t-slot cutter because even the smallest won't fit into the opening (0.350"), and unlike a straight t-slot there is no opening to start the cut from the side. The slot itself is 0.540" from side to side and 0.200" in height.

I'm guessing I'll have to grind a special tool (sorta like a boring bar or maybe a gear cutter) but any advice would be greatly appreciated. I'm wondering if there is some sort of off-the-shelf cutting tool I'm unfamiliar with.

I have a (cheap import) rotary-table/dividing head. It's not the machining that has me stumped, it's what tool to use (and how to make one). I'm guessing it will be something like a cutter for making gears, only much smaller diameter.

For now I'm just doing the rest of the basic squaring of the part, milling of the t-slots, and prep-work for cutting the dovetails. Eventually I have to get to the actual compound slot, though. Here's a pic of the straight t-slots that I milled today. That was straightforward. Machining cast iron is certainly messy (I've got all my ways covered with paper towels, and I also run the irritatingly noisy shop-vac continuously to catch most of the dust) but man is it a joy to work!



Any and all advice much appreciated.

Best regards,
--
Rex

P.S. I was surprised to find there doesn't appear to be a Logan forum on this site!

 

[tertiaryjim]

How about a single point tool with it centered in a four jaw chuck.

 

[Rex Walters]

The casting is about 11" long and quite heavy. My 11" monkey-wards lathe might just barely be able to swing it, but the work holding and counterbalancing would be a challenge. I can imagine the profile to grind in the tool, though. Maybe such a tool in a boring head on my vertical mill might work. The circle diameter is just a little under 3".

Thanks!

 

[Rex Walters]

Wait. That won't work (boring head in the vertical mill). It's not like boring a hole from the outside. There's a step to get past. There's no way to gradually increase the diameter of the boring head swing each pass. I may end up attempting to hold it on a faceplate in the lathe as you suggest. At least that way I can gradually increase the depth of cut. Makes me sweat just to think about it, though — that's definitely at the extreme limits of what my lathe can do.

I'm going to ponder this a bit more. I may have to punt and make it in two pieces (unlike the original part).

 

[coolidge]

Turn a locating pin for your rotary table, flip it upside down and mill it from the other side.

 

[Rex Walters]

The other side has the dovetail ways. Really don't want to cut through those! <laugh>

 

[coolidge]

Well it made perfect sense after breathing in 2 cans of break cleaner fumes tonight...doh! I believe my Grizzly G4003G has a circle machined in the top for inserting the bolts and presumably for lowering the cutter to mill that slot.

 

[hman]

Looking at your original post, I see that there's a round access hole going out the bottom of the groove. This is how the T nuts are loaded. How about first cutting a circular groove from the top, equal to the width of the top edge, and as deep as the final T slot will be. Then flip the part over, centered on a rotary table, cut the round access hole from that side, and then feed a T slot cutter in from there?

 

[george wilson]

As stated,you can mill the round T slot with a rotary table if your lathe can't swing it.

I will mention that years ago in an emergency,the headstock and tailstock of lathes were sometimes set upon riser blocks that were machined to fit the headstock,tailstock,and the ways they were set upon. The old lantern tool posts were increased in height by means of a thicker washer at their bases,which the rocker set in. These special tool posts could be purchased. In fact,I have one,but it is for a lathe more like a 16" swing,at least.

While you can't get these things these days,you could make some for yourself. Just a headstock riser would be enough to do larger swing work,and a taller way to mount tools. The gears on the back of the headstock would not be usable,but you don't need them at all to turn something like that round T slot. Just feed manually-which I would do anyway on this type of job.

Jacking up the headstock is still a common practice among metal spinners even today.

 

[brino]

hman's got it in post #8
-brino