Increasing Friction

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ctwo
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Increasing Friction

Post by ctwo »

I am modifying my vertical cymbal stand to add a boom section for better adjustability. The joint comprises two 2" diameter, 1.125" long "hockey pucks" of 12L14. I make an offset bore through the diameter to slide 7/8" diameter tubes. I will make a threaded hole to accommodate a threaded shoulder bolt to clamp the joint and tubes into position.

I prefer the positioning not to be notched or detented, but rather infinite. I am concerned that the smooth machined flat surface will not provide enough gription. Since my surface grinder can create a wavy surface if I desire, I was considering grinding with a series of passes that all run through the pivot hole.

Any thoughts?

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liveaboard
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Re: Increasing Friction

Post by liveaboard »

I think a smooth machined hole will work best.
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GlennW
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Re: Increasing Friction

Post by GlennW »

Keeping the bolt hole as close to the tube bore as possible will help. (almost intersecting)
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Bill Shields
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Re: Increasing Friction

Post by Bill Shields »

Make them wider so that you can have two knobs per clamp.

I have seen them where the pipes are knurled...but they to not seen to hold up for long.
Too many things going on to bother listing them.
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rmac
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Re: Increasing Friction

Post by rmac »

Bill wrote: Make them wider so that you can have two knobs per clamp.
But with two knobs it won't pivot any more ?????

joint.png

Anyway, if I read ctwo's question correctly, he's more concerned about slipping between the flat surfaces of the two hockey pucks than he is about the gripping action on the tubes. I agree that it would be better if those surfaces were somewhat rough. Or maybe a thin rubber washer between them would help.

Another idea would be to copy the clamps that they use on magnetic indicator bases, sort of like this:

holder.jpg

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ctwo
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Re: Increasing Friction

Post by ctwo »

Russel is correct - I think the tubes will have significant clamping force, especially if I move the bolt as far away as possible, but that then decreases the contact area of the two discs as the angle between the tubes is increased. The indicator base clamps like that are too complicated.

Getting set up to drill the bolt hole, then I think I'll cut the slot with a milling saw.

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rmac
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Re: Increasing Friction

Post by rmac »

ctwo wrote: The indicator base clamps like that are too complicated.
Yeah, a little bit. Four parts instead of two. Looks like you're almost done anyway.

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parts.jpg
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Bill Shields
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Re: Increasing Friction

Post by Bill Shields »

rmac wrote: Wed Nov 30, 2022 7:50 am
Bill wrote: Make them wider so that you can have two knobs per clamp.
But with two knobs it won't pivot any more ?????


joint.png


Anyway, if I read ctwo's question correctly, he's more concerned about slipping between the flat surfaces of the two hockey pucks than he is about the gripping action on the tubes. I agree that it would be better if those surfaces were somewhat rough. Or maybe a thin rubber washer between them would help.

Another idea would be to copy the clamps that they use on magnetic indicator bases, sort of like this:


holder.jpg


-- Russell Mac
sure it will...you make the 'pucks' rectangular and put 2 knobs in line with each other.

guess I am not explaining myself correctly.

We have a similar problem with the microphone stands we use at church...they never stay put. I can imagine the problem of stacking a cymbal on the end of a long arm then whacking it with a stick or mallet...
Too many things going on to bother listing them.
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liveaboard
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Re: Increasing Friction

Post by liveaboard »

I see now, it's the flat surfaces that you're thinking about.
I would bypass friction and go for a a positive lock, like milled V grooves radiating from the bolt holes that interlock when the knob is tightened.

Oops, did someone say "too complicated"?
Nah, never.
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Bill Shields
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Re: Increasing Friction

Post by Bill Shields »

I completely missed that also...was looking at the cylinder clamping....which is where I have experienced problems.

Maybe bead blast the contact surfaces....?
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jwmelvin
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Re: Increasing Friction

Post by jwmelvin »

OP’s clamp reminds me of a Noga indicator clamp I have, which is a pretty efficient way to affix two cylinders using two forked, angled end caps and a central washer:
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ctwo
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Re: Increasing Friction

Post by ctwo »

So I asked our mechanical engineer. He tossed a roll of 3M traction tape at me. https://www.3m.com/3M/en_US/p/d/b40066689/
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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