Repairing Cross Slide Screw, Need Suggestions

[BWS Arms]

You can get new replacement parts from Victor. I have purchased several parts from them. It’s not the cheapest route but it’s nice to have the original parts on the lathe.

 

[David2011]

You can get new replacement parts from Victor. I have purchased several parts from them. It’s not the cheapest route but it’s nice to have the original parts on the lathe.

Thanks. That was the first route I tried. I submitted a written request through their website. They didn't respond to my request. The guy that answered the phone when I called a couple of times, prior to deciding to replace the cross slide screw, was not very friendly either.

Doing it myself was not inexpensive. The Acme screw was $75 shipped, the Acme tap was $46 plus tax and the bronze for the nut was $34 plus shipping and tax so after shipping and taxes I have at least $160 in the job.

I started making some parts last evening with the new parts that I made and couldn't be happier with the results. I still have a problem with the cutting tool dipping on heavier cuts. The carriage is lifting off of the bed so I have to figure out exactly where the slop is and what to do about it.

 

[ddickey]

Did you the check the carriage gibs or anti-floaters?

 

[David2011]

Did you the check the carriage gibs or anti-floaters?

Yes, I checked the front one since that’s where the problem seems to be. I can get an .008” feeler gauge between the strip and the lathe bed near the chuck but 12-15 inches away from the chuck the gap reduces to .006” and its a very tight slip fit at that point. I’ll check the gib in the back today.

I’ve about concluded that it’s not a real big deal. For parting I can lock the carriage and the problem with the tool dipping is eliminated. For turning I’ll just have to work with the limitation. It’s only affecting the maximum DOC I can take and that’s not even a very big thing. I’m used to a bench top machine so being able to take off .040”-.050” is about all I want to remove at once anyway. After that dodging hot chips isn’t much fun.

Last night I made some rods with 3 different diameters, a threading relief and 7/16-20 single point threads on both ends and it was SO much easier than with the bench top machine.

 

[BWS Arms]

I never had a problem ordering from Victor. They were helpful and shipped quickly. They had everything I needed in stock in CA. except one thing. They ordered it from the factory in Taiwan and I had it in about two weeks.

 

[David2011]

Thanks; I appreciate the info. If I need anything else for the lathe I’ll try again but I’ll call instead of relying on website communications.

 

[ltlvt]

If your concerned with strength and holding surface for the tapered pin, you could do a shrink fit on something like a 3/8" dia. fit up. First chamfer the major diameter's of both pieces, assemble, and weld up the V after a few evenly spaced tacks. Then turn the weld down to the shaft o.d.. This is of course, provided you have the equipment for the task, or a freind to help you out. I've had good luck going this route. Mike

I agree with the machining but if he doesn't have means to weld it then the same process you suggest except braze it or silver solder it. Either would hold up very well to the twisting of the screw. The majority of the force is going to be pushing the tool bit into the rotating shaft, so I don't see a problem with either of the methods. I am getting ready to do the same thing on my Clausing 5913. I already have the Acme rod that I bought from Green bay MFG and I plan to make my own nut out of cast iron. My old Clausing 100 had a cast iron nut from the factory and the nut wore but the screw did not. So, I replaced it with cast iron. the Screw in the Clausing 5913 is razor sharp in the middle and has a bronze nut from the factory. it is my experience that the nut is much easier to make than the screw. I just bought a left-hand Acme tap off of Ebay from Chinabay and they work great. Somewhere around $15 or $20 for each one. I (also (made/repaired) the half nut on my Clausing 100. Looking forward to follow up on David2011's repair.

 

[David2011]

I agree with the machining but if he doesn't have means to weld it then the same process you suggest except braze it or silver solder it. Either would hold up very well to the twisting of the screw. The majority of the force is going to be pushing the tool bit into the rotating shaft, so I don't see a problem with either of the methods. I am getting ready to do the same thing on my Clausing 5913. I already have the Acme rod that I bought from Green bay MFG and I plan to make my own nut out of cast iron. My old Clausing 100 had a cast iron nut from the factory and the nut wore but the screw did not. So, I replaced it with cast iron. the Screw in the Clausing 5913 is razor sharp in the middle and has a bronze nut from the factory. it is my experience that the nut is much easier to make than the screw. I just bought a left-hand Acme tap off of Ebay from Chinabay and they work great. Somewhere around $15 or $20 for each one. I (also (made/repaired) the half nut on my Clausing 100. Looking forward to follow up on David2011's repair.

See posts 40, 42 and 44. I have the means to weld. Brazing or silver soldering would affect the heat treat of the 4140 screw. I didn't want to weld this. The only concern about torque was that I have a pressure type knurling tool that I have to use frequently and that requires more torque than any cutting operation. I will be adding a scissor type knurling tool but as a volunteer machinist for a battleship restoration I needed to get the lathe operational again as early as I could. Mostly I make parts for the deck guns.

The Acme thread was mated to the hand wheel end of the new shaft using Loctite 603 which cured for two days before being installed. Two days was because I had to do some other things; not because it needed that long. I have several hours on the lathe since the repair and the cross slide feels like it's on a factory new machine. I'm hitting dimensions within a thousandth without intermediate measurements. I can back off .010" and the tool doesn't drag on the work. Before the repair I had to back off just over 1 full turn of the hand wheel and depths of cuts were irregular because the old threads were so worn.

 

[gard]

I started making some parts last evening with the new parts that I made and couldn't be happier with the results. I still have a problem with the cutting tool dipping on heavier cuts. The carriage is lifting off of the bed so I have to figure out exactly where the slop is and what to do about it.

Where is the cutting tool relative to the center of the carriage (right to left)? If the tool is near the center, I think there should be no force causing the one front corner of the carriage to lift. I guess if there is a lot of radial force on the bit it could cause the back of the carriage to lift up which would cause the cutting point to lift (not dip). In any case you might find the problem goes away depending on where the cutting point is above the carriage and how it is sharpened.
I have seen some photos where people have added weight to the back of the carriage to keep it down. My lathe has a taper attachment on the back and I have not seen any lifting in the back. I do tend to try to lock every movement I can when using the cutoff blade,

 

[ltlvt]

The cross slide screw and nut project is finished and I could not be happier with the results.

While I had things apart I also shimmed the cross slide gib. I had seen the cutting tools dip several times on heavier cuts and had broken 2 or 3 carbide cutoff bits. The gib was adjusted as tight as it would go so it clearly needed some help. Since I bought the machine I've felt like it was probably used for very little other than facing or other cross slide type operations for a very long time. That is reinforced by all of the wear in that area while the rest of the machine seems to be much tighter. These repairs may reveal weaknesses elsewhere, though. I measured the space between the gib and the dovetail in the cross slide with feeler gauges and thought a 12" x .008" feeler gauge would be about the right thickness. When I test fitted it, it turned out to be a little too thick and I ended up using a 12" x .006" feeler gauge. I shortened the long feeler gauge as required and smoothed the ends. After degreasing the gib and feeler gauge with brake cleaner I glued them together with Loctite 603, installed them and let the Loctite set for 10 minutes. Everything around the back side of the gib had a generous amount of oil on it so I wasn't concerned about the Loctite joining things that shouldn't be joined. Just to be sure, I pulled the gib out after 10 minutes, reassembled it and the cross slide and adjusted it. A dial indicator showed no side to side movement after shimming yet the cross slide could still be move in and out by hand pressure. Great start!

The protruding piece in the above photo was removed and a barely touching skim cut made on the surrounding area so the new nut would have a solid place to rest. Apparently I didn't take a picture of the flattened area. I'll back up and show some photos pf the process. The old nut was well worn as as mentioned earlier, seated on the round piece above so it wanted to rock back and forth as the screw was turned. The gap between the nut and cross slide is visible here.

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The power cross feed gear was pinned with a single tension pin and was easy to remove.

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The wear in the old threads is pretty obvious. The peaks of the threads are much narrower in the middle than at either end.

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I cut the threads off of the screw with a hacksaw. It cut pretty easily; definitely not very hard steel.

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After facing the rough end I drilled and reamed the end to form a socket. It was at this point that I realized I had no way to measure the ID of the bore since my snap gauges only go down to .500" and my target was .402". I had previously written .401" but that was just a mistake on my part since the reamer was not as I remembered.

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It was about this point where I incorrectly thought that I could do a good shrink fit and only got about 1/2" of the pin into the socket before it was stuck. I recovered by machining back a bit of the previously prepared Acme screw and got a perfect slip fit on the replacement. I glued it with Loctite 603 and it had three full days to cure before I got the nut made. The nut was made of aluminum bronze instead of the usual 936 bearing bronze because I couldn't find a small piece of 936 bronze. The aluminum bronze came from Speedy Metals and was about $34 plus shipping for a piece 1" x 1.25" x 3". It was about 1/8" oversized in all directions so there was plenty of excess to clean it up to my 1" x 1.25" x 1.5" starting point. After truing up the entire 3" piece I cut off 1-1/2" and cleaned up the sawn end. The blade is 1/16" x 4" and I went slow, spinning it at 70 rpm. Somewhere around 150 rpm would have still been plenty slow.

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After cleaning up the end I chamfered the corners. The chamfer bit is a Bassett carbide tool, made in the USA. That was the first time I had used it after buying it late last year. It worked very well. All of the milling and drilling was done on my Jet-16 mill-drill since the quill and spindle are out of my Index mill at the moment for new bearings and a regrind of the R-8 taper. The other half of the bronze was in the other end of the vise jaws to keep the load balanced.

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Tapping the block went well enough for the screw that secures the nut. I drilled to where the centerline of the cross slide screw would later be drilled and tapped it with an M8-1.25 spiral flute tap. That was my first indication of the toughness of the aluminum bronze. I used lots of Tap Magic EP-Xtra. The thread was beautiful even if a little difficult to cut.

The big hole for the leadscrew was located by putting the nut on the cross slide, assuring that it was squared up and using a shop made transfer punch to mark the location of the Acme screw hole on the end of the nut. The hole was spot drilled and then completed using progressively larger bits until the desired diameter was reached. Some of the larger bits had unknown histories and got pretty warm in the process. The hole for a 5/8" acme thread is just over 1/2" and a size for which there is no bit shown on my Starrett chart so I went to the next larger Imperial size. The new nut is 1/4" longer than the original for a little more surface area in the thread so I wasn't concerned that the hole was a few thousandths oversize.

Tapping was a chore. I got the tap started straight while the nut was still in the mill's vise but once it had made several turns I laid the nut on its side for more clamping surface. As it got deeper it tool a lot of force. Unfortunately I didn't have a tap handle big enough so I ended up using a socket and ratchet. That saved a lot of work and time, though since I was only turning the tap 1/8 turn at a time and that took my full body weight leaning into it. Finally the pressure began to ease and the tap went all the way though.

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After deburring it was picture time.

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With the original nut and screw the backlash measured .122"; almost a full turn of the hand wheel. With the new parts installed it measured just .001". The lead screw gets tighter just before is screws all the way through the nut so I expect that as it wears in the backlash will increase to a more normal for new machines level.

Time to make more chips and see what else the machine needs.

Excellent job and fantastic documentation of what and how you did it. If I understood correctly you joined the new lead screw Acme thread to the old hand wheel end by a slip fit and Loctite 603 and no pin? If so I may just do the same on mine. Currently I am working on solving the lift problem of the saddle with Moglice.I should complete the machining this week and apply the Moglice later. I will start on the screw and nut after this is complete. Thanks for doing such a great job documenting how you did yours. Many years later readers will reap the benefits of your efforts.