Suggestions for boogered-up drawbar threads

[toms73novass]

I am going throught the parts I got with my SB 13". What I have noticed is that the collets will not thread down fully in the draw bar. They go in about 5 turns and then stop.

Upon further inspection you can see where the threads are boogered up. Any suggestions for a fix?

-tom

[eng4turns]

1) Make up a single-point thread tool with a good handle on it and use it manually to try to chase the threads.

2) Chuck the drawbar up in your independent 4-jaw, center it, and chase the threads with a single-point. Tricky part is picking up the thread since they are very fine and internal, thus hard to see.

3) Cut off the threaded part, braze on a new, shop-fabricated piece with a bigger OD than the drawbar for machining allowance, set up in 4-jaw, turn down the OD, bore and cut new threads.

4) Make a whole new drawbar from scratch.

5) Buy a replacement.

Have I exhausted the possibilities?

Ed in Florida

[eng4turns]

Just thought of another one:

6) Take an old collet or just go buy a cheap one and modify the threads into a chasing tap. Use a dremel tool to carefully cut some grooves and then relieve the teeth behind the cutting edge. Stone the cutting edges. Weld a handle across the other end. It's a one-time use tool so it doesn't have to be perfect. On further thought, this is probably the first thing I'd try.

Ed in Floriduh!

[Riderusty]

I've used eng4turns' suggestion #2 of chasing with a single point tool in the lathe with good results. After lining up the tool point in the existing thread I slowly turned the spindle by hand. Its a fine thread and not much had to be removed to clean it up.

Tom B.

[sicero]

Set it up and bore all the threads out past the five. Sacrafice one of your duplicate collets and use it with valve grinding compound until a normal one will fit. Make an external slug with the threads on it to use with the compound. Valve grinding compound has saved me a lot of money when I run Catapillar tractors. One big fine thread nut might be $200. They have the same accountant as Monarch. lol Kenny
ps I am fresh out of ideas.

[toms73novass]

Thanks for all the suggestions, much appreciated.

At this point I do not have a functioning lathe so ...

I do have 1 duplicate collet that I might give a try.

I just need to disect your response. I think what you are saying is to cut slots with a dremel parallel to the keyway that already exsists on the collet.

How many?

Then you mention to relieve the teeth behind the cutting edge. The cutting edges are were the slots intersect with the threads....correct?

To relieve them, you are saying to taper from where the dremel cut on the thread is to where the next dremel cut is?

Sort of new at this stuff....

Thanks again

[eng4turns]

You've got it right. About four or five cuts with the Dremel perpendicular to the threads and then relieve (reduce the threads) back around to the next cut. Leave about a 20 or 30 thou land behind the cutting edge.

Oh, when using the Dremel try not to overheat the metal.

Ed in Florida

[toms73novass]

Ed,

Thanks for the tip.

-Tom

[Clive603]

How long is the bad thread portion?
Rest of the way, coupla turns, part of a turn or a strip along several threads.
If its just part of a turn or a strip along several careful application of a swiss file will sort things well enough. Most sets have one about 1/4 wide with a very shallow triangle profile, mine are about 3/32 on the thick, safe, edge and nominal sharp on the other. Thread restoring files are quite effective too, a bodgers tool I know but sometimes a bodgers tool is the best response.

Bottom line is that the drawbar only screws in so far hence the 5 good threads will continue to hold. Full nut depth is 6 or 7 threads (usually) and I believe standard stressing calculations suggest that only the first 4 or maybe 5 fully engaged threads can carry any load so a less than perfect fix will be acceptable.

Clive

[toms73novass]

It appears where the collet stops threading there is a double "thread" which prevents it from going further. The concern I had with it is that when I put in a collet and tighten down an item in it, that it does hold the item as I am approaching the point of the binding. However, I do not know if it would be tight enough when a tool is cutting the item and if it would slip in the collet.

[Toms Wheels]

Without seeing the installation I suspect that 5 threads is where the collet has grabbed the work for the last 40 years. I'd suggest you spend $10 and buy a thread file, that has the internal files on the end. Make a wood block that will give you some leverage in the drawbar. You could also rig a tap with the same TPI pitch and a wood dowel with a groove to lay the tap in. If that falls then clice the collet threads.

[strokersix]

Depends on what the damage is. If it's only a couple dings in the threads then above suggestions should be tried. If it looks like mine where the threads are worn and/or deformed any attempt to chase them will probably make it worse. You might be able to modify by cutting off the damaged threads if there are good threads deeper. Alter other parts as needed to extend the draw tube by the amount you cut off. Add thread relief inside the tube if necessary.

I'm out of luck making a replacement draw tube until I get my QC box repaired so for now I use it as-is and try not to over tighten.

[toms73novass]

once again thanks for the ideas. I totally forgot about thread files....

Good idea about a large wood dowel and insert the thread file.

Thanks , Tom