Teach me about alignement pins!

Patrice Lemée

Patrice Lemée

Joined
Aug 13, 2002
Messages
5,703
Every time I use them, this time for a filing guide, the fixture is always a little "stiff" for lack of a better word.

Aside form the obvious that the pins have to be aligned, is there any trick to getting them right?
Also, how much oversized do you ream the hole and how much undersized for the one that I press fit the pin in?

Thanks

Patrice
 
The best way I know to get them aligned correctly is to stack and clamp the work then deep drill the holes. Use a body drill size for your holes they are clearanced enough to allow easy slippage on and off. (called "clear" in the chart for some reason)

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Jason
 
Jason, guess I was overdoing it a little by reaming the holes to size then. :o

As far as drilling them both at the same time, I had a hard time with that using the mill vise. I tried to put the 2 pieces in there that were exactly the same size but when I tighten the vise down it clamped the bottom piece fine but the top one was just loose enough so that you could slide it fro side to side. I guess the jaws open up at the top a little.

Thanks for our help.

Patrice
 
Patrice Lemée;7745967 said:
when I tighten the vise down it clamped the bottom piece fine but the top one was just loose enough so that you could slide it fro side to side. I guess the jaws open up at the top a little.
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I use a wooden paint stir stick, cut in half as a "liner" on each of the vice's jaws, they will take up the slack and hold it tight. As well as keep your piece from getting scratched up from metal on metal contact. :)

Patrice Lemée;7745704 said:
how much oversized do you ream the hole and how much undersized for the one that I press fit the pin in?
Click to expand...

Forget that mess! on the undersize one. drill and ream to the EXACT pin diameter at room temp. Freeze the pin in your freezer over night. heat the hole to 500ºF and then insert/press the pin in and let the temps normalize. It wont come out...
 
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Thanks Sam, actually my main problem was not how to do it but more what I was looking for as far as clearances are concerned. As Jason pointed out I guess I was trying for too tight a fit.

Patrice
 
I have also placed a copper wire between the milling machine jaws and the part with wire pointing vertical on one jaw.
Some like to go .001 undersized when pressing in a pin, you could also go to the same diameter as pin. I usually do that and just hammer in with red loctite.
Chris
 
I will add to the above comments by telling you how I made my filing jig. It is made from 3/4" stock and has 3/8" bolts

I took my 2 pieces of stock and carefully aligned them and clamped together. I then welded the 2 pieces together on the ends only and removed the clamp.

Drill the hole for 1 bolt using the appropriate tap drill (5/16" in my case) and drill completly through both pieces. Without moving the pieces, drill through the top piece only with the correct drill for the bolt that you are using (3/8" in my case).

I then drilled through both pieces for the alignment pin and reamed -- again without moving the piece. Now do the same thing for the other side.

Now, with the pieces still welded together, tap your holes by placing the tap in the hole that was drilled to the bolt size (the 3/8" hole in my case) and tap the other bar. By doing it this way, you will have perfect alignment as the hole in the top bar guides the tap for tapping the bottom bar.

With the pieces still welded together, surface grind, flat grind, Attach carbide (in my case) or what ever is needed to make sure both are true to each other and grind off the welds.

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Hope this makes sense and is helpful
Brian
 
Thanks for taking the time to write all the steps Brian, I'll use this when I build it this week-end.

Patrice
 
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