Lathe Cross Slide Problem

[EdK]

(05-29-2014, 07:56 PM)PixMan Wrote: Do you have a depth micrometer that would span the dovetail on the bottom? if not, use a parallel (bar) of a known dimension and measure down to the bottom of the pocket you milled (and subtract the thickness of the parallel if you used one.) Measure with a micrometer or height gage the overall height of the cross slide top. Subtract, you got the thickness. You need that anyhow to get the right length of engagement on mounting screws.

Add thickness found to the .926" existing thread center line. Now you have the starting "?2" dimension.

Now measure the depth from top of cross slide to existing lead screw (top of it), add 1/2 the screw's diameter and you have "?1" dimension.

What is the difference between the two center line lengths? Mill down or shim up as required.

Thank you so much Ken. I'll have to read that a few times to fully absorb it but I think I've got the gist of it. Oh, and I do have a depth micrometer that will span the dovetails so I'm good to go.

Ed

[EdK]

Finally got some work done on the cross slide. I had to bore out that hole that was knurled to get rid of the knurls so I can press a plug in it to fill the hole. Next is to make the plug and press it in.

Ed

   

[EdK]

I got the plug made and want to make sure I'm headed in the right direction for this press fit.

Hole = .7375"
Plug = .7379-.7381"

Cross slide is cast iron.
Plug is 12L14.

The thickness of the cross slide at the hole is a bit less than .75".

Would putting the plug in the freezer for awhile shrink it enough to make it a bit easier to install or is the piece too small to gain any benefit by cooling it? I don't want to heat up the cross slide.

From what I could tell by using Mr Google, the .0004 to .0005" oversize of the plug is within the range for this situation. I'm just looking for a snug fit, it doesn't need to be super tight but it shouldn't be able to be moved just by hand strength alone.

Any thoughts before I butcher my cross slide?

Thanks,
Ed

[f350ca]

You won't move a half thou interference by hand. Doubt if cooling the plug 40 or 50 degrees from room temp to freezer temp will help much.

[PixMan]

Easier to warm the slide by a couple hundred degrees and get more cast iron expansion that you would contraction of steel dropping 50 degrees.

Just warm it up a little bit with a propane torch. Good enough.

[EdK]

Do you think I need to support the cross slide, as shown in the first image, when I press the plug in? Or is the 3/4" thick cast iron strong enough to handle the pressure unsupported, as in the second image?

Thanks,
Ed

       

[f350ca]

I'd support it, very unlikely you'd crack the cross slide without support but if you did you'd never be able to kick yourself hard enough. The support shouldn't need to he hollow as in your sketch, doesn't the plug sit flush on the bottom?

[EdK]

(06-13-2014, 05:00 PM)f350ca Wrote: I'd support it, very unlikely you'd crack the cross slide without support but if you did you'd never be able to kick yourself hard enough. The support shouldn't need to he hollow as in your sketch, doesn't the plug sit flush on the bottom?

Thanks Greg, I suspected that would be the answer so I just got done making the support. I assume aluminum is fine.

It needs to be hollow because I made the plug about .050" over in length so I can press it flush to the top of the cross slide then mill the bottom side down enough to take a light skim of the cross slide guaranteeing the plug and cross slide surfaces are on the same plane for mounting the lead screw nut.

Ed

[Mayhem]

Like Greg, I'd support it as well. No point risking that 1 in a million crack!

[EdK]

I made some progress on the cross slide today. I got the plug pressed in and the three holes almost done. The middle of the three is supposed to be threaded for a set screw and I grabbed the wrong drill bit and drilled it for a clearance fit instead of a tap drill. Not a big deal, I'll just use a M6x1 instead of the 10-32 I was going to use. I still need to slot the screw shank hole in the left hole. I've got the screw head hole slotted but couldn't slot the shank hole in the same setup so I need to flip it over and mill that from the bottom side.
Ignore the far right hole. It's for a Gits oiler and not part of the cross slide fix.

Ed

EDIT: I guess I didn't screw up the hole for the set screw. I went to drill it out for a M6 tap size and realized I hadn't drilled it larger than a tap size for a 10-32 thread. So now the hole is tapped for the 10-32 set screw.