Making a Cross Feed Screw for a Lathe or Mill

I seem to be missing something with your thread depth formula.
The book calls for 1/2 the pitch plus 0.010" thread depth for a ten pitch or coarser thread.
This would be 0.060" for the ten pitch thread.
I understand that you used wires to get the correct pitch diameter but why do you need the
extra 0.010" root clearance?
 
I seem to be missing something with your thread depth formula.
The book calls for 1/2 the pitch plus 0.010" thread depth for a ten pitch or coarser thread.
This would be 0.060" for the ten pitch thread.
I understand that you used wires to get the correct pitch diameter but why do you need the
extra 0.010" root clearance?

Oops!

You are correct! My wrong. It did work. The old screw thread was at approx. .070" deep too. Couldn't measure it exactly.

I did check the nominal thread depth at .060" per my thread program, but when I started checking the root diameter to the major diameter with tolerance, I was coming up with a depth from .0575" to .06515-.070" deep. I added .010" to the .060" thinking it didn't already have the .010" clearance added. So I cut it a little deeper than it should have been. My apology for my mistake.
Here is a snapshot from my program.
Capture121217.PNG
 
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Since you used wires to check the thread and it wasn't a centralizing thread there shoudn't be any problems.
It's just more room for oil to flow in for lubrication.

I have seen free to use programs, like you show, on the net. They sure are nice.
They showed me a number of incorrect ideas I have of threads.
Sometime in the future I would like to make a acme tool gauge for internal threading or perhaps a measuring tool
that uses trig to get the tool tip width ( flat ).
I was thinking a 20tpi acme could be handy, standard only goes to 16tpi, and that program gave all the information for internal and external threads,
including the tool flats.
Found a paragraph in The New Machinists Handbook 1955 edition, page 10-8, that gives a formula which uses trig and a simple measurement
to get the tool flat or another gauge that uses a depth mic. So, another project is to make a tool holder that clamps to the jaws of a dial indicator or a mic to get the measurement at a known distance from the flat of the threading tool.
 
Since you used wires to check the thread and it wasn't a centralizing thread there shoudn't be any problems.
It's just more room for oil to flow in for lubrication.

Exactly!

My thread program is in the Downloads section of this forum if you want a copy of it. I used basically the same output information that another manufacturer uses for the software they sell. Every one of the formulas used in my program came from one of several AISI/ASME standards on screw threads, Acme, and Stub Acme threads. And also the Federal screw thread standards, too. All readily available for a price. A co-worker of mine helped on the excel file contents to make it into what you see. The program will take any number of threads. The only thing you would have to do is add a thread wire size for a 20 pitch Acme thread to get the M.O.W. to come out correct.

Ken
 
Hi Ken,
Looks good. I'm considering making a short crossfeed screw for one of my machines as well. What are your thoughts on using 4140? Especially on thread quality compared to threading the 1144 stress proof?
Chris
 
Nice job, I've been making screws for industry various sizes and lengths up to 4 metres and when screw cutting these i made up
split collars reamed to the required size with 1 or 2 tangential socket screws for locking on the bar and one on the side that goes between the jaws of the chuck to take the load of the cutting force, that way one does not need to over tighten thus saving scroll
overload and avoid slipping
 
Hi Ken,
Looks good. I'm considering making a short crossfeed screw for one of my machines as well. What are your thoughts on using 4140? Especially on thread quality compared to threading the 1144 stress proof?
Chris
I think you would be much happier with the results using 1144 T,G, & P Stressproof. Don't get me wrong, I've machined a lot of stuff out of 41xx materials and work with this grade of material almost every day of most of my life in the design work I do in my real job. Occasionally run into a piece or two that will stress relieve itself after machining. Mainly on long parts. If you're look at the wear properties verses 1144, it will last longer. The real drawback on 41xx grades, it's hard to find it with a ground OD without sending it out to a grind shop and have it centerless ground. If you are looking at wear issues, look at using drill rod if the OD is not over 2". It's expensive! But will yield you with a screw that will last a lifetime. I have on my Sheldon lathe I made over 35 years ago. Has zero wear in the screw and maybe .005" in the nut. Of course I keep it oiled once in a while and clean it every ten years. I've had 3" OD lead screws made years ago out of 1144 stressproof that got very good life. They ran in a bath of oil with a bronze half nut. Ususally get about three to four years out of an nut on the trepanning machines they were on. The leadscrews, well I've seen ones in near new shape that were well over ten years old and still running. Much for the ranting.
 
So pardon my dumb questions, but I'm so impressed with this:
- when I hear people making the lead screw nut & having to buy an expensive reverse thread tap, did you alter the tool orientation & cutting direction on like a boring bar style tool?
- on the lead screw threading, when you said you went to either side a bit for a smaller progressive bite, does that mean the threading tool advances straight in, or the compound still has some angle?
- what type of insert holder/tool did you use for both ID & OD operations
- what do you recommend for an anti-backlash arrangement on the nut, do you have a pic of that
 
So Ken, do you use a thread gage? And if so, what kind? I see there are the individual blades and the plate style. Any pros or cons to either?
 
Ken,

All the thread calculator programs say the thread depth is .060". Where did the extra.010" come from?
 
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