how to create 4 pieces of equal length and square ends?

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dansawyer

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I am making a tracking device for astrophotography. The drive box will be 6 inches long and 2 inches top and bottom. It is my plan the top and bottom connect on the ends of the sides, The drive shaft will connect through bearings on the top and bottom.
The objective is to make the top and bottom as parallel as possible. This to me implies the sides should be of equal length and square. The exact length is less critical than the 4 side pieces be of equal length. My current plan is to cut the sides from longer pieces of 3/8 aluminum 2 inches wide.
I have a South Bend 9 with a milling attachment.
My plan is to cut the pieces as close as possible. Align the pieces on a surface plate and then firmly clamp them. Then carefully drill 4 holes near the corners and bolt them together. This should make a cube with the sides square.
Next I will square up the sides on the milling attachment and carefully mill the first end with the side of a large mill cutter. I will then flip the cube and mill the second end.
Is this a practical approach? Is there a better way?
 
I think firmly clamping the parts together then mounted into your lathe (assuming you have a 4 jaw), square it up then face off the end, flip and repeat for 2nd end.
K.I.S.S method/approach is my suggestion.
 
Latinrascalrg1 said:
I think firmly clamping the parts together then mounted into your lathe (assuming you have a 4 jaw), square it up then face off the end, flip and repeat for 2nd end.
Click to expand...

I would add that with a 6" long piece, you should center drill and support with a center in the tailstock. If I understand correctly, the center drilled spot (will only be on 2 of the 4 sides) will be hidden by the top and bottom when assembled.
 
It sounds like it's time to find an inexpensive milling machine. :)

But I think what you propose will work.

You might concider changing the design a bit. Starting out with a piece of 2 x 2 square solid stock and pocketing it out might be easier than trying to align the top and bottom. 3/8 x 2 rectangular bar is not going to be flat, it always has a bit of a valley in it.
 
JimDawson said:
It sounds like it's time to find an inexpensive milling machine. :)

But I think what you propose will work.

You might concider changing the design a bit. Starting out with a piece of 2 x 2 square solid stock and pocketing it out might be easier than trying to align the top and bottom. 3/8 x 2 rectangular bar is not going to be flat, it always has a bit of a valley in it.
Click to expand...

I created the plan to find a milling machine and ran squarely into 'clean out your garage first'. :(

What do you mean by "pocketing it out". I was planning on creating a jig for the 4 sides 1 3/4 square and then stair stepping the side pieces around the jig. The top and bottom pieces would be 2 1/4 square.
I would clamp the top and bottom pieces together and drill / mill the bearing holes. The centering if the bearing holes in not critical as long as they are aligned with each other.
 
Sometimes things don't go as planned :)

Pocketing is just removing any material that is not needed from the center of the part, leaving the walls. In other words, you just create a box from a solid piece. We do it all the time on the CNC equipment, but also easily done on your equipment. May not take any longer than trying to assemble the pieces.
 
Pocketing would keep the pieces from shifting over time, as would dowel pins. Clearance holes are normally some .008- .012" larger in diameter than the fastener to allow for some misalignment. Spring or roll pins could also be used. If mating parts are stack3ed and drilled as a unit, the roll pins will remove the necessity for precision reaming.
 
A lathe and a square 5-C collet would work with an end stop in the collet.
 
If all 4 pieces are bolted together then just hold them in the chuck and face off all 6 sides.
A 3 or 4 jaw can be used, if three jaw the off set balance just needs a slower speed.
For the length the sides of the jaws can hold the items not just their ends. ie, set the assembly diagonaly in the jaws.
Check the face of the chuck, it should be flat so that can be used as your reference surface.
I do this all the time but then again I have no formal training.
 
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