[How do I?] Making Feed Screw And Associated Parts

[stomp10]

Hi All!
I am in the process of making a small mill feed screw for the Edelstaal Lathe. Original equipment was a 7/16" x 20TPI LH threaded screw.

I have sourced the easiest material I could find. 1\2" cold rolled turned to a couple thousanths under .4375". Bought a Polish made adjustable die for cutting the threads. At this point I have about a half inch of fairly perfect looking threads on the end of the stock now, (Looks perfect to my inexperienced eye, anyway.) and I think I'm ready to start threading the rest of it as soon as I get the rest of it to diameter.

Plenty of cutting oil, and taking my time making the threads. Forward 1/4 turn, back 3/4. I'm really impressed with the results so far. Only another 15" to go and I hope the die holds up... Going to use lots of oil...

For the part that the screw will thread into, I got a hold of some 954 bronze off of flea bay. I was balancing cost\functionality and, I realize that this probably isn't the ideal mix of materials, but my question is will either of the 2 dissimilar materials pose a problem as far as longevity of the parts, premature wear, etc, or am I just asking for trouble?
Anything else I should be aware of here?

Not oilite bronze, but I have no problem using lube on it if need be.

Should the CRS be hardened\tempered after machining, or can I leave it as it is?

I'm struggling with understanding materials and compatible material that goes with other materials and such.
Any understanding anyone could share would be most appreciated.

If it wears out too soon, I'll make another from the correct materials

 

[joshua43214]

Oil lite bronze requires special machining and finishing, it is good you are not using it.
I would think 954 should be fine, dunno. Most folks use 660 I think.
You will not have a problem with dissimilar metal. Trouble only arises in the presence of an electrolyte. So unless you plan to use salt water as a lube, this is a non-issue. You lathe is filled with dissimilar metals in contact with each other, they are protected by oil.

You can try to harden the screw, but you will almost for sure end up with a bent screw. Better to start with some pre-hardened material and single point thread it (you might be able to thread with a HSS die though, never tried it).
The screw will wear out before the nut anyway, bronze has better wear characteristics.

You can lap the screw to the nut with Bon Ami scouring powder. There are probably other products. Bon Ami is a non loading abrasive, it can be entirely removed and not penetrate the metals. Use something else at your own risk, most abrasives will go into the bronze and continue to wear the parts. Make the two a tight fit and just run it back and forth with a drill dumping Bon Ami on it for an hour or so.

 

[Kernbigo]

I used to make lead screws for j&l thread grinders, we always re used the nut, bored it out and rebushed it. The lead screw were ground from fresh material and ground to fit the nut by trying many times tell you got the fit you wanted.

 

[Kernbigo]

contact Steve Wells he sells them

 

[Chipper5783]

I made a cross slide lead screw for my smaller lathe. I found it quite a challenging project. I think the actual screw was about 12" of thread (8 tpi LH, Acme). I made it because I could not find threaded stock material (and I like to make stuff). I was using my larger lathe, to single point the new screw. The problem I had was that I could not eliminate the tool push - even with a very keen HSS tool having lots of rake. The follower rest that came with my lathe, and I believe is correct for this machine had never been used, or even fitted to the machine (I've owned the machine over 30 years). Anyway, fitting the follower rest is yet another project, and I have not quite gotten to it.

I finally worked out an extremely unorthodox follower rest (deffinately no pictures taken) for the last couple of passes. I reused the old nut - it is a split, so easy to adjust. The end result was very satisfactory. The little lathe now works great. It ended up taking me quite a long time. Yet another project that again helps me appreciate the craftsmanship of people who figured out how to do this sort of task in the first place (machinist were probably doing this sort of thing 150+ years ago, faster and better than I did with a lot less kit).

The pictures below show both the old and "new" screws.

 

[tertiaryjim]

Chipper
I had a similar problem making a new cross-slide screw for my lathe.
I made left and right-hand threading tools with a small amount of positive top rake.
After cutting to depth with the left-hand tool I then cut the flank of the thread with the other tool.
This required much less tool pressure and worked well.

 

[stomp10]

Thank you for all of your replies. Much appreciated.
Boy, am I glad I asked the question.
I figured, make the threaded parts, put them into service and move on to the next job. It never would have occurred to me to lap them. Makes perfect sense though if you want nice smooth operation.

Joshua, I am assuming that the BonAmi is used dry?

Chipper, by the looks of it, that screw really needed to be replaced. Nice job on the new one too!

 

[joshua43214]

Joshua, I am assuming that the BonAmi is used dry?

I have always used it dry when lapping threads. I have mostly done it one all-thread used for mechanical parts in furniture. Lapped threads really have a nice tactile feel.
I was looking for a video I saw a while ago doing it, and came across this one

They are using lapping compound and transmission oil. It certainly looks less messy than Bon Ami...
Taigs have been around for a while, we would know if this ruined the screws.
Maybe someone knows a source for non-loading lapping compound. The only compound I have ever used around the shop are pastes made from diamond, garnet, or alox - all of which will load into the work

 

[stomp10]

Thanks, Joshua.
I particularly like the fact that the BonAmi will not load into the work, and I think I am going to do it your way. Not too worried about mess, that's what the shop vac is for. And really not that messy if its a dry compound cleanup.
The other feed screws on the Edelstaal lathe are a little sticky in places... They really aren't worn at all. I don't think this machine had a lot of use over the last 35 years or so. I might try this method to polish them up and get them spinning nicely again.

Thank you so much for sharing. This is a great tip that I will store in my memory banks for later use...

 

[Chipper5783]

Thank you for all of your replies. Much appreciated.
Boy, am I glad I asked the question.
I figured, make the threaded parts, put them into service and move on to the next job. It never would have occurred to me to lap them. Makes perfect sense though if you want nice smooth operation.

Joshua, I am assuming that the BonAmi is used dry?

Chipper, by the looks of it, that screw really needed to be replaced. Nice job on the new one too!

Lapping removes only a small amount of material (as in 0.0001" - 0.001" is a lot to lap). I'd figure Joshua is correct, that it will give you a nice smooth feel - but I'd recommend you get the size correct first. You can check to see how uniform a thread you have by measuring over 3 wires that fit part way down the thread flank. The actual size of wires or the reading on your micrometer do not matter. You are only using this method to compare one part of the thread to another. Cut until the thread minor diamter is correct, if you ground the tool full width, then the thread should fit. If not, then shift the tool over slightly and increase the width. Measure - test - figure out where material needs to be removed, test the fit on the pin end (where the thread will end up being cut away - or make the screw slightly long with the intent of cutting off the extra) - measure - test - figure out where material needs to be removed, . . . . and so on.

Jim's approach of cutting the two flanks seperately sounds like a good plan (I am not convinced that it will eliminate the tool pushing the work away at the mid point), but it will reduce the tendency for the work to deflect away from the tool.

I have never lapped any threads (only thing I ever lapped was valves into their seats) - the goal is to get a good surface finish on the thread. I find with a good tool and decent material (not 1018), one can get a very nice finish. If a person were to lap a thread wouldn't one need a female nut that was sufficiently oversize to allow lapping compound into the thread? This would not be an issue with a split nut (as in a lathe cross slide nut), but wouldn't a one piece nut end up being loose? You could make up a "lapping" nut and a "real" nut? Anyway, like I said - I've never lapped threads.

On the Edelstaal, if some of the screws are sticky in places, maybe there is some sort of an issue (debris, damaged threads) - they probably didn't come from the factory that way. Figure out the problem and address it.