Blade Retention Screw Thread Pitch

[hybridspecies]

Happy New Year! I'm getting ready to tap a #5 Blade Holder for a blade retention screw and it seems that most around here recommend either an #8-32 or a #10-32 screw. I'm leaning towards a #10 set screw, but I have always been told that coarse screws such as the #10-24 work better than fine screws in softer metals, such as aluminum, to resist stripping (the base material) under tension. An exception to this would be when tapping into a thin-walled metal, in which case a finer thread would be necessary for sufficient wall engagement, but the wall thickness of the blade holder where I intend to tap (beefy section near the top) measures 1/4" so that really isn't too thin a wall (would support 6 threads on a #10-24 vs 8 threads on a #10-32). Is there another reason then why the #10-32 should be used? Does Tim use tempered aluminum perhaps? I didn't even see a #10-24 screw or tap set offered in the store. Thanks.

[xl97]

my suggestion is go smaller.. if it strips out.. you have more than enough room to drill and re-tap.

that being said.. the 8-32 screws have been used around here fora long time.. and I havent heard of any problems.

Most of the parts/process is a 'tried & true' method.. if there were problems it would have been brought up before =)

[hybridspecies]

Hi xl97 and thanks for the response. I understand your logic, but just the fact that the smaller screws can strip out makes me want to use a larger screw in the first place. I've read a couple posts from folks claiming that their #8-32 failed under heavy dueling. Also, I own an Ultra Saber and the blade is starting to stress fracture where it comes into contact with the #8-32 set screw. The larger screw should, in theory at least, be able to distribute the pressure over a wider area of the blade thus reducing the occurrence of stress fractures. I picked up a piece of 1.5" scrap 6061 aluminum tubing this afternoon at the local metal shop and will experiment on it before I tap the blade holder. Unfortunately the piece is only 1/8" thick, but that should still be enough to gauge whether a coarse or fine thread is needed.

[Jay-gon Jinn]

I use the 10-32s screws on the same location on those styles you're thinking of using, and I've never had one strip.

[hybridspecies]

For closure (in case someone else ever has the same anal retentive question) my experimentation on the scrap pipe indicated that the 10-32 stripped more easily than the 10-24. I stuck a piece of conduit in the pipe after drilling/tapping and turned the set screw in until it stripped (actually in both cases the pipe threads stripped not the screw threads). I repeated this three separate times and the results were always the same although the number of turn fractions varied slightly. In all fairness, though, no one would ever need to secure a polycarbonate saber tube as tightly as I did the conduit. HOWEVER, in another test I repeatedly smacked the conduit against a palm tree and was surprised to find that the 10-24 worked loose much quicker than the 10-32 did. I repeated the test after re-tightening and had the same result. The 10-32 never budged or stripped. So in conclusion, while the 10-24 is definitely more resistant to strippage than the 10-32, use the 10-32 if you duel and don't want to keep re-tightening the saber blade - the 10-32 should hold adequately. The alternative would be to use loctite on the 10-24 for the best of both worlds, but that would make blade removal more difficult and is unnecessary based on my findings.