Old Heavy 10 - How much backlash is too much on the crossfeed?

I'm working on a 1949 Heavy 10 I picked up this week and there seems to be quite a bit of backlash on the feed screw on the crossfeed.

If I zero the dial, it'll turn to about 70 thousandths before the slide moves. I know she's an old machine and I can deal with it, but I'm concerned that if the screw or the nut is badly worn it might lead to bigger trouble if I don't address it.

FWIW - The dial was changed over to the large style. (Which if I'm not mistaken, uses a different feed screw). Does that require a different nut as well? I'm wondering if the previous owner might have overlooked that?

TIA for any words of wisdom.

-Rich

If the total lost motion is confined to the feed screw and the nut, It really does not matter how much backlash is present. 10 thou or 70, you still need to "take it up".

and once taken, the unidirectional motion should be "stiff".

Good work will result with your attention.

But, if there is uncertainty, with moving screws or nuts, only troubles will follow...

check carefully!

I have about a 1/2 a turn of play (about .06) in the cross slide of my 1942 Sheldon model L, and it can make good parts.

Just have to remember to take the play out of it.

If you have the money just go ahead and replace the screw and nut. I fought with mine for 25 years before I wised up.. Life is too short to "screw around"

I forgot who I bought my newly made screw from but I can find him if you would like me to.

It could just be that the nut is loose. When I bought my 10K a number of years ago at auction, and experienced machinist (he really is) cam over to show me how much slop was in the cross slide - maybe a turn and 1/2!

I just kept it to myself, and when home, cleaned it out a little and tightened down on the screw that holds the nut (that you take out, to use the taper attachment on these). It still has almost 1/2 turn, but as others have said it has no bearing on the work. .005" or .050, you still have to take it up.

PS, one other area for lost motion is between the shoulders of the screw and the retainer, what ever that may be. (As opposed to all of it being in the screw threads) SB does not use ball bearings in the cross slide screw, so there will always be some lost motion.

smt

If a gap opens up between the dial and the retainer when you back the screw out (after removing backlash by turning Cf screw in), measure the gap with a feeler gauge and shim between the screw shoulder and the retainer .005" less than the measured amount(you want a little play). This is assuming you do not have a taper attachment (different screw).
As said above, check the bronze nut mounting screw for tightness. Visually inspect the screw at the middle of threads and end of threads(end threads wont have wear,the middle threads may visually look thinner). If the threads and nut are worn, replace both. My grandfather had a saying, well, one of many, "if a machine is worth keeping...it's worth keeping well", in other words, fix it proper. Good luck.PB

A ton of backlash gets on my nerves as well. I can easily tollerate a small amount, but tons of it can be a pain in the ass.
Here is what I did, and it didn't take very long:

http://www.practicalmachinist.com/vb/south-bend-lathes/quickie-repair-worn-crossfeed-nuts-273712/

Frank

Rich, I'm going to disagree with most of the posts, .070 backlash is way too much, when you get to the point of trying to part something off, you just might find it a bit difficult and stressful let alone all that winding back and forth, just not good. Lets be good machine repairmen and bring the lathe back in as good of specs as we can. The backlash on the cross feed should be .003 or less to be in SBL spec, yes many work way past that and so have I, but what fun is that...lol start your learning curve by repairing the screw assembly and refitting the mount and dials to spec. read the SBL install forms for a new screw for instructions on the large dials and fitting for backlash removal, no shims, no glue, just work slow and steady. The nut is the same for with or without large dials or taper attachment.
"SB does not use ball bearings in the cross slide screw, so there will always be some lost motion"
Stephen, I'm sorry but that is just incorrect. They did use bearings in the large dials, the earlier small dials did not, but most newer post 40's 10L's had the large dials, and these are fitted with slight preload, so there will be no lost motion from a proper fit dial and mount bushing. All backlash will be in the allowed spec of the nut and screw fit which as stated was .003. Most if fitted properly will make this spec with some wear in the nut/screw. A new 4-G nut, a replacement screw blank, and refitting the dials and mount bushing will take care his problem. Rich, you need to tear down the screw assembly and make sure you have all the parts, bearings ect, by the parts sheets and then rebuild it. I'ts not that hard, just takes time and effort. A silky smooth cross feed is worth the effort and makes it safer and less stressful to use your lathe. After the cross feed do your compound and add bearings to it...they didn't use bearings in the compound, but it's very nice to have them in there.

Steve Wells

On my South Bend 11" I had trouble with the nut not being secured. Things got a lot better when I tightened it up. --- best wishes --- Allen