How does on press in small pins straight?

WobblyHand

WobblyHand

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I'm trying to make a barrel nut wrench for an airgun. It's a pin spanner wrench. There are 6 pins arranged in a hexagonal pattern. Approximate pin circle diameter is 11mm. The pins needed are 2mm. I bought some undersized 2mm dowel pins. I drilled the holes deeper than the pin needs to be. Used a center boss (goes in the bore) as a stop for my arbor press. Measuring the pin circle yields a variation of 0.2mm between adjacent pins. It appears the pins aren't going in straight, although they are being started straight. These are steel pins pressed into 6061. I'm using a #48 drill for the hole. Probably doing a lot of things wrong, but this has been interesting nonetheless. Here's a picture of my test piece to the right, with part of the real piece waiting for me to figure out the magic sauce.
PXL_20231009_195608858.jpg
PXL_20231008_203925343.jpg
1 inch 6061 stock, 3/8 1144 for the rod.
 
So the pins are cutting into the aluminum? Or are your original holes not perfectly aligned?

I'd think you could make a steel fixture, with the same hexagonal hole pattern using slightly oversized (slip fit?) holes, to hold all six pins parallel while being pressed in. That would help keep the pins consistent.
 
rabler said:
So the pins are cutting into the aluminum? Or are your original holes not perfectly aligned?

I'd think you could make a steel fixture, with the same hexagonal hole pattern using slightly oversized (slip fit?) holes, to hold all six pins parallel while being pressed in. That would help keep the pins consistent.
Click to expand...
Not sure which at the moment. Holes were drilled on the mill using the bolt circle function. I can practice that again, maybe the pattern is off. I see evidence of the pin being either squished, or the the pin not going in straight. Without xray vision, its hard for me to tell. These undersized pins are only 12L14 which isn't the toughest stuff. I could get 18-8 stainless, which is harder according to McMaster. Caliper readings seem to indicate pin deformation on some pins.

Could be the hole isn't deep enough considering the difference in diameters between the pin 1.985 mm and the hole due to a #48. I drilled the holes 7mm deep and pressed the pin in 6mm. I have room to drill 8mm holes. Of course that's a 4:1 depth to diameter ratio, maybe the hole wandered? It's a skinny drill. Maybe I was too aggressive in drilling. I didn't ram it in, but it was a slow process. I did use WD40. Perhaps pecking might yield a little better results?

I could make a steel fixture to hold the pins. But it can't have deep holes, only about 2mm.
 
If the pins are deforming, one option is to use a 2mm drill and use CA to glue the pins in place rather than pressing?
 
I would think you could make a rod that holds the pins, just drill it a little oversized, and just shallow that half the pin fits in. Use a magnet on the side to hold the pin in and use your drill press or mill to hold the rod and push the pins in straight. The rod and DP only needs to start the pressing straight finish with a small hammer, or turn the rod over and press in. you can even drill the other end for the length of stick out, and it will bottom out when in at the correct height.
 
.003” pinch on that small of a pin is a lot. How about a #47 and some green loctite?
 
I only have two thoughts on it, Wobbly. Either the drill isn't stubby enough or isn't evenly ground and it's wandering, or you have underestimated how much slop is given to wrenches to allow a working fit.

Pressing pins into aluminum is usually very easy to do, the alloy is practically slick and should guide the pins very well given the right fit, which I believe you have: 1.93mm hole and 1.985mm pin should be fine. I can't see anything wrong there.
 
pontiac428 said:
I only have two thoughts on it, Wobbly. Either the drill isn't stubby enough or isn't evenly ground and it's wandering, or you have underestimated how much slop is given to wrenches to allow a working fit.

Pressing pins into aluminum is usually very easy to do, the alloy is practically slick and should guide the pins very well given the right fit, which I believe you have: 1.93mm hole and 1.985mm pin should be fine. I can't see anything wrong there.
Click to expand...
Hmm. New stubby drill. Could be an underestimation of the design problem, not going to deny that. I will go back and take a look at things again. Will measure the drill bit and each pin. Making a new test piece doesn't take much time.

Pressing 0.25" pins in aluminum is easy. But I had nice reamers and got a nice fit. These are tiny pins and blind holes. Don't quite have the right size holes nor do I have tiny metric reamers. Probably need to acquire some more metric drills.
 
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