Sanding mandrels

[Chasper]

I usually make pens in semi large batches, at times up to 100 in a batch. I have found that it is easier to turn all of them, usually on between centers bushings, then sand all of them. For sanding I make sanding mandrels to do multiples at once. I usually use an aluminum tube, wood dowel or derlin rod for a mandrel. I make the mandrel slightly smaller in diameter than the ID of the tube and long enough to load 4-7 pen sections at once for sanding. I cut tubes to short lengths to serve as spacers. It doesn't matter if the fit is not tight like a turning bushing, I just use them for sanding.

I want to cut threads on some of the more used mandrels so that I can screw a nut on to lock it down firmly. Finally, I'm getting to the question I'm here to ask. I have a foot long 1/2 inch thick wall aluminum tube, about .26 ID, just enough for a standard mandrel to slide inside. I want to cut threads in the 1/2 in rod/mandrel and I don't know much about thread cutting. Do I use a 1/2 in die and will that take a 1/2 inch nut? It seems like a bigger die and nut might be needed, I don't want to buy the wrong size die.

 

[howsitwork]

Could you give a sketch or photo of what you are trying to achieve?

I read this as you want threads on the outside of the tube? If so a 1/2" die maybe too small and might cut through or leave it too weak to use . Generally the rod to be cut is SLIGHTLY SMALLER than the thread you want as the metal will extrude slightly in the die as you form it.

 

[Woodchipper]

Keep in mind the aluminum might flex at that length.

 

[Curly]

Chasper you can cut the 1/2" thread on the end of your tube as the wall is plenty thick enough. Maybe sand/turn it down to .492 before threading. You have a choice of 1/2-13UNC or 1/2-20UNF (Unified National Course or Unified National Fine if memory serves) The coarse nuts are more common but the threads are deeper. You should be able to find fine threaded nuts which are shallower and if not graunched won't be a problem. If you are wrenching them until the veins in your forhead pop maybe stick with coarse. Personally because of my aircraft background I would use fine. Sparingly use a thread lube, drop of oil or a little paste wax when using the mandrel. Use an aluminium cutting oil like Alumicut to cut the threads with.

 

[southernclay]

I love this idea. Do you just use for sanding or finish on the mandrel as well? Seems like something Rick Herrell could help with.

 

[Chasper]

A picture always helps. I want to cut threads on the non-live end. There is a conventional turning mandrel holding the sanding mandrel in place on the powered end. The sanding mandrel is 1/2 inch diameter with a 1/4 inch hole. That leaves plenty of room for cutting threads. The sanding mandrel is 12 inches long, it is not going to flex, but even if it did flex a little that would not be a problem, I only use it for sanding.
In the picture it is loaded with 6 turnings and some spacers. I plan to use a longer tobe, about 15 inches long to be able to sand 10 at once. I will probably use coarse threads and will turn the part to be threaded down to .492, what size die should I buy? I have the thread cutting information I need from Curley, thanks.

 

[Curly]

The die will be either 1" or 1 1/2" depending on who you buy from and what die handle you want to get/have. 1" is probably going to be more useful to you for any other threading you will most likely want to do. Get a split round die.

Has the "e" in my name been awarded for excellence?

 

[Chasper]

The die will be either 1" or 1 1/2" depending on who you buy from and what die handle you want to get/have. 1" is probably going to be more useful to you for any other threading you will most likely want to do. Get a split round die.

Has the "e" in my name been awarded for excellence?

Excellence Exactly

 

[thewishman]

Gerry, thank you for the germ of an idea! I'm grabbing some drill rod that's almost perfectly sized for the tubes I need to pump out in volume.
I'm switching from buffing to Magic Juice for my finishing and can get a lot of blanks loaded on a 25" rod mounted on my metal lathe. That will speed up my polishing considerably.

 

[howsitwork]

Aluminium will definitely extrude as cut. LOTS of paraffin or WD 40 works brilliantly as a cutting lubricant making your life easier and the quality of thread is improved too.

 

[egnald]

Using a Set Collar or Split Set Collar for clamping could possibly be an alternative to cutting threads. That way you could use the same shaft for even a single blank if you needed to. I have used a pair of collars with a spring in between them to apply pressure and clamp a varying number of parts onto a shaft before. - Dave