Holding small square stock for lathe operations?

[ninefinger]

Let me lay out my particular issue. I have an 8" 4 jaw that just won't clamp down on 3/16" square stock so I can make one end cylindrical and drill and tap for 2-56.

I've tried a slit collet in the three jaw, one steel and one aluminum and they have all ended in the little bit coming free even under very light cutting pressure.

Any other shop made solutions for this? Failing the lathe I'm seriously tempted to use the cnc mill to do this operation....

I'm going to go put the kids to bed and think about it some more, hopefully I can get this done tonight ( I have 10 of these to make..I had 12 but one has walked off somewhere. )

 

[OrangeAlpine]

Sort of shop made solution. I have a 3" four jaw that I hold in the 3 jaw. Recently got fancy and threaded a steel stub to screw into the little 4 jaw, now I hold it in the 3 jaw by the stub.

Bill

 

[stevehuckss396]

For making sparkplug insulators I saw up Corian countertop material into 1/4 inch square bars. I made a mandrel to hold them for turning. Once you tune it in it becomes a quick change holder.

 

[ninefinger]

Thanks Steve, I like that little holder idea and may use it, but making a square hole is where I'm falling apart! I guess I could try and broach it with a homemade cutter but that would be yet another whole new learning experience.

I think my problem with my little collets was they were too soft and the corners bit into them , making their grip get loose. When I first tried it I had a longer bar through the collet and it worked fine but now that the parts are short the load on the corners was too much.
I still want a way to do this operation on the lathe but...
The mill is actually seeming more and more appealing for this one job the more I think about it:

I get to drill with a good high speed for the #49 drill (like 3400 rpm) versus the lathe which gets a bit scary at its top end of 1800rpm

I can easily set up the parts to be all the same length
and the outside round is just cosmetic so I can polish them up after if needed.

only downsides I see:

The tool changes from milling cutter to drill and then tapping (using the spindle to guide and turning by hand).
Getting the setup right on center for these small pieces could get tricky.


I think I'll wait till tomorrow and see if there are few more ideas that come in before then.

Mike

 

[kvom]

If you have a 5C collet chuck then you can get square collets for it. Alternatively you can get the square collet, put it in a hex collet block, and chuck in the lathe with a 3 jaw chuck.

Another solution would be to start with round stock, turn the round spigot, then use it to chuck in a collet block to mill the 4 flats.

 

[ninefinger]

I think I've found my makeshift solution - I'll know tomorrow when I try.

Tap holder - I realized it has a 4-way split and is designed to hold onto the square end of a tap. I have one that seems to be just the right size and I can trap a depth stop in there to help with the setup.

I'll fill you in tomorrow on how it works out. Off to bed now that I can sleep having at least a hope of a quick solution.

Mike

 

[n4zou]

Mill a 3/16 slot in a peace of round stock as if you were making a key way in it(it's size is not important). The slot depth should be cut a little less than 3/16. Chuck the round stock insuring one jaw will contact the part to be turned in the slot which will hold it in the slot as you turn it to size. After you have the part to be turned aligned to centre in the chuck (the round stock will be off centre of course) you only need loosen the one jaw holding the part in the 3/16 slot you milled in the round stock. Not only will the part be held tightly in the slot your production speed will be greatly increased.

 

[AussieJimG]

That is a great idea n4zou, I hope I can remember it when I need it. And I am sure that I will at some time.

Jim

 

[Woodster]

Simple solution. Round stock, cut to length, split down center then mill 45 degree V down the center of each half. I'll do a sketch if you need one.

 

[stevehuckss396]

Thanks Steve, I like that little holder idea and may use it, but making a square hole is where I'm falling apart!

Mike

Just drill the corners before you mill. The corners dont need to be square.

I like the tap holder idea. Good idea!

 

[ninefinger]

Thanks for all the suggestions. I ended up using my tap holder to hold the parts while I drilled them and turned them down to 1/8" diameter. I did not realize just how small the parts were for the team build engine when I signed on. Pictures do have a way of skewing our perspective sometimes.

If I were to do this again I would do n4zou's suggestion of milling a slot in a bar and holding it in the 4 jaw. It would be much more secure. I had to be very careful to take small cuts so as to not cause the part to jump out of the tap holder (which happened on my last piece - got over confident... :fan: )

Here is the tap holder "chucking" up a part - its clamping on ~ 0.280" of material and I turned down 0.25" of length. Unfortunately my tap holder has a larger diameter at the handle end so it effectively has a stick out of ~2" which reduces its rigidity as well. If I was doing 1 part I would have chucked up the knurled part in the 3 jaw but as I was doing many copies I wanted to be able to use the collet and have a depth stop behind it for rapid part removal and replacement.

and the finished parts

Mike