Scroll Saw Won't Hold Tension Under Power

[JPG]

Me too!

[redleg]

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I use a faucet removal tool to remove some tension pins/roll pins. I think I got mine from a plumbing supply but lots available on google for less than $10.

[algale]

^That's a pretty good idea, redleg, thanks!

[JPG]

I like that better than the four handed banging approach. Gonna have to make something similar.

[algale]

Progress made! I clamped a ten pound dumbbell (not to be confused with JPG ) to the arm. I also discovered that by lowering the arm as much as possible, I could push the arm up against the lip of the casting (see yellow arrow in photo). This gave some stability and I drove the pin out.

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No wear to the tension pin (also note arm against casting to allow pin to be driven).

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The biggest surprise, however, is the tension rod. Although irretrievably bent at the top, the hole for the tension pin has no visible elongation or wear (ignore grease).

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There is still slop in the connection between the pin and the rod (1/16th?) but it seems designed?

[JPG]

It retrospect that makes sense. The arm needs to pivot there(ever so slightly). 1/16" seems excessive. The arm holes need to be snug.

We gonna conclude the loosening was due to the 'warp'?

Likely a combination of both.

[algale]

It retrospect that makes sense. The arm needs to pivot there(ever so slightly). 1/16" seems excessive. The arm holes need to be snug.

We gonna conclude the loosening was due to the 'warp'?

Likely a combination of both.

Intuitively, I believe that the bent threaded section of the tension rod would change the geometry of the cam/lever in the down position and would therefore have an adverse effect on the cam/lever's holding ability.

As for the slop in the tension pin and the hole through the tension rod, I'll throw calipers on both so we can quantify it accurately. It seems any slop would mean the blade isn't at full tension at the beginning of the up stroke and the beginning of the down stroke.

[JPG]

It retrospect that makes sense. The arm needs to pivot there(ever so slightly). 1/16" seems excessive. The arm holes need to be snug.

We gonna conclude the loosening was due to the 'warp'?

Likely a combination of both.

Intuitively, I believe that the bent threaded section of the tension rod would change the geometry of the cam/lever in the down position and would therefore have an adverse effect on the cam/lever's holding ability.

As for the slop in the tension pin and the hole through the tension rod, I'll throw calipers on both so we can quantify it accurately. It seems any slop would mean the blade isn't at full tension at the beginning of the up stroke and the beginning of the down stroke.

Compare them to the new parts.

It should be free to rotate, not wiggle.

Greater tension on down stroke than up stroke if slop.







Should be free to rotate, not wiggle.

[algale]

The old parts seem to measure .220 inches (hole in tension rod) and .194 inches (tension pin). Those measurements don't seem to correspond to any obvious imperial fractions. Be that as it may, it has less than half the slop (.026) that I estimated (.0625).

[JPG]

The old parts seem to measure .220 inches (hole in tension rod) and .194 inches (tension pin). Those measurements don't seem to correspond to any obvious imperial fractions. Be that as it may, it has less than half the slop (.026) that I estimated (.0625).

A 3/16" tension pin will measure larger than 0.1875" when 'expanded'. Remember it is a compression spring that is placed in tension when squeezed.

0.0325" seems very sloppy to me.

Measure the holes in the arm? 0.188?