Pivot washer gap

H

Hubert S.

Joined
Dec 14, 2019
Messages
1,437
I did a test piece the other day to practice peening a slipjoint pivot pin. I used a piece of paper micarta and drilled the hole for the washer with a 1/4" end mill. I put a drop of superglue in the hole and inserted a small piece of 416 stainless rod, then drilled a hole offset by about 1mm from the center of the rod and reamed it with a #41 reamer. Before peening the 3/32" pin, I used a small burr to taper the hole on either side. The good news is that the pin blended into the washer, the bad news is that I have a gap. The picture makes it look really big, but I honestly did not see the gap until I took the picture and zoomed in.

What is the best way to avoid this gap? Can I peen the washer to fill the gap before peening the pin?

E7pvvZS.jpg
 
Measure your rod and your endmill. See what the difference is.

Also be sure your set up when milling is rigid, also check your run out.
 
If you look carefully you can see your hole is not round
 
AVigil said:
If you look carefully you can see your hole is not round
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The picture was taken at an angle, so the hole should not look round. I cannot tell whether the hole or the rod is more out of round, but I think the rod is probably not very precise. Maybe I need to get some oversize material and turn it down for a better fit. Is there a better tool than an endmill for drilling a shallow flat bottomed hole? I have measured the run out on the mill, and it is a small fraction of a thou.
 
Hubert S. said:
The picture was taken at an angle, so the hole should not look round. I cannot tell whether the hole or the rod is more out of round, but I think the rod is probably not very precise. Maybe I need to get some oversize material and turn it down for a better fit. Is there a better tool than an endmill for drilling a shallow flat bottomed hole? I have measured the run out on the mill, and it is a small fraction of a thou.
Click to expand...
I would check your end mill diameter.
 
Do you lock down the table when you mill a hole like this? Can leadscrew backlash cause non-round holes? Asking/don't know.
 
Thank you Adam and Mike for your suggestions. I think I know what I did wrong. The one step I did not mention in my first post because I thought it was not important is that I pushed the washer in with a piece of rod that I had put in the chuck. I think I must have had the washer on there crooked and/or off center, and when I pushed the rod down, it probably cut or dented the relatively soft paper micarta. When I made the first washer, I just quickly deburred it with a file instead of putting a proper chamfer on it.

I made a new test piece, this time I put a bigger chamfer (about 20 thou) on the washer before cutting it from the 416 rod on the lathe. I took extra care to make sure it was centered on the hole and with the chamfer I could feel it drop into place. I could not push the washer in with finger pressure, so I pushed it in using the same rod I used the first time, but it seemed to go a bit easier. I have not put a pin in it, just quickly ground it flush to check for gaps. I'll practice it a couple more times to see if I can get a good result consistently.

V9y8H93.jpg
 
I just held a set of calipers up to the first picture and the hole is round, the metal is egg shaped
 
Britt_Askew said:
I just held a set of calipers up to the first picture and the hole is round, the metal is egg shaped
Click to expand...
The picture was not taken from straight above, so a circle should appear as an ellipse. I think it's impossible to tell whether the hole or the metal rod is round or not from that picture. I know the rod is not perfectly round, but I think it's close enough where you won't notice it as long as there is no gap.
 
You really do not want that disc with a hard pressed fit. You want to be able to slide it in with out any difficulty.

If it is to tight a fit the adhesive will be pushed out. You want glue under and around the disc.

Sanding the rod to fit before cutting the disc will give enough room for glue.
 
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