Trying to improve the holding power of an alum on alum rod clamp

[helmbelly]

Have you thought about bead blasting the gripping surface on only the interior portions?

One product I learned about here is Bonderite for aluminum. Very easy to use and might be a good finish for your parts.

Very interested in Bonderite - thanks for the tip. What would be the goal of bead blasting? I realize it would give a polished surface but my question would be is lack of polish really contributing to a weak clamp? The metals we are clamping to - are generally pretty clean but can be scarred up a bit. the more polished they were the more I would want polish true. I can bring them to a high state of shine with buffing wheels - I'll def learn something if I put adhesive fine grain sandpaper on one and polish the other!

 

[helmbelly]

I don't see why it wouldn't work. The hard part is machining the groove for the o-ring in your bore, but it should be easy enough with a properly sized keyseat cutter.

I wanted to make a sketch, and ended up spending more time in Paint than it probably would have taken to do a real dimensioned design


View attachment 373570

Pete huge thanks for drawing. it makes it so clear. I was following you I can see now. This is a great approach for overcoming a taper or adapting to what may be slightly differing tapers while maintaining straight grab if there is no taper at all. I have never made an inside cut quite like this (I'm not a machinist, just learned by doing) but it seems like a 4 jaw chuck on the lathe with boring bar. This is very interesting. I got a 4 jaw for my rotary table but its too big for my lathe. But I think I could make a holder for this I could clamp into 3 jaw. I really want to try this

 

[rons]

Very interested in Bonderite - thanks for the tip. What would be the goal of bead blasting? I realize it would give a polished surface but my question would be is lack of polish really contributing to a weak clamp? The metals we are clamping to - are generally pretty clean but can be scarred up a bit. the more polished they were the more I would want polish true. I can bring them to a high state of shine with buffing wheels - I'll def learn something if I put adhesive fine grain sandpaper on one and polish the other!

The intent of my suggestion was to do just the opposite. Pocket the surface with little impact craters so that there would be a gripping surface.
I use Ballotini Impact Beads on aluminum 6061. I ran my finger over the surface and it feels like a 1200 or 2000 grit paper. It does surface harden
the surface and a Bonderite coating is easy to do. I think it's the easiest thing to do before altering dimensions with sandpaper.

Don't know if different grades of sand or walnut shell would work better. I only know Ballotini. Looking up close the surface looks like some of the media
inbeds into the surface.

The Bonderite metal etch solution is something that I only use once. The plating solution is something that I reuse. Comes in yellow and clear.

 

[BoxcarPete]

Pete huge thanks for drawing. it makes it so clear. I was following you I can see now. This is a great approach for overcoming a taper or adapting to what may be slightly differing tapers while maintaining straight grab if there is no taper at all. I have never made an inside cut quite like this (I'm not a machinist, just learned by doing) but it seems like a 4 jaw chuck on the lathe with boring bar. This is very interesting. I got a 4 jaw for my rotary table but its too big for my lathe. But I think I could make a holder for this I could clamp into 3 jaw. I really want to try this

If you feel comfortable enough with the IP aspect, send me a PM and we can dig into specific design points if you'd like a little more help. The basic idea is to control the volume fill ratio, but it's not trivial to get it right once tolerances get involved.

 

[EPAIII]

I have worked with a lot of photographic equipment, both amateur and professional, and am at a loss to think of any that would use a tapered tube. I really am curious.

I don't know which of those two holes is for the tapered tube, perhaps even both. I don't think you have a problem due to aluminum on aluminum. More likely it is just the geometry due to the taper. That would reduce the contact to just a small ring at the larger end of the taper. If you could just bore the hole to match the taper, then the problem should just disappear. But, apparently that is not possible. Or is it? Apparently this is not a one time only job so if the taper is constant from one tube to the next, then a matching reamer could be purchased and used to taper the hole. It would probably be a custom made reamer but over many units it would pay for itself.

Another thought: I wonder if one side of the clamping area could be changed into something more like a hose clamp which would be flexible enough to conform to the taper. This might involve milling the aluminum down to a thin strap-like section but with a block left on the end for the clamping screw. This may or may not be possible as we do not know the loads that will be present.

Here is a photo, I'm no expert but just with my own experimenting when I've roughed the mating surfaces by roughing with a file or sand paper it holds less well than a polished surface - which I suppose is because like a taper - it's just more surface in contact area and also no curfs to roll and shift under load.

I like the idea of non slip tape. i looked at that link - thanks. they make quite a few _I'll give them a call and see if I can get someone on the phone like we used to during the last century.

I'll try cigarette paper right away, I guess you just mean rolling papers like rice paper? This part is used outdoors so that works I'd need to find a water tight fix.I do plan to over bore it and anodize, I'm going to google polyurethane strips.

Thanks


View attachment 373539

 

[EPAIII]

Yet another idea would be to simply cut a saw slit half way from one end of the hole to the other. This would be perpendicular to the slit that allows it to be a clamp and go all the way from the outer edge to completely across the tube. That would split it into TWO clamps, each on a different section of the tube. Each would have a tightening screw and each would grab the tapered tube at a different diameter. It would also allow a bit more flexing as I suggested above so each of those two contact areas may be larger than what you are getting now.



This may be the simplest idea yet and it just may work.

 

[reggie_obe]

Sorry we have a provisional patent on this but I have a partner and agreed that we don't put info online until we have the product in the pipeline. I make camera parts for over 10 years now and have been ripped off really bad overseas.

Fair enough, most honorable sir.

 

[tmt]

Why not just move the clamping bolt position toward the end where the taper is smaller. Hence when tightening occurs, the lager end will engage first and remain in good contact while continued tightening will engage the smaller diameter and provide a more uniform force along the shaft. The point that provides the best uniform clamping force is, may take a little experimenting.

 

[eKretz]

Why not just move the clamping bolt position toward the end where the taper is smaller. Hence when tightening occurs, the lager end will engage first and remain in good contact while continued tightening will engage the smaller diameter and provide a more uniform force along the shaft. The point that provides the best uniform clamping force is, may take a little experimenting.

Just as long as there's no variance between parts...

 

[tmt]

Just as long as there's no variance between parts...

What do you mean VARIANCE? It said it was tapered

Just as long as there's no variance between parts...

What do you mean by VARIANCE, microns, thousandths, inches, feet, miles? The OP stated that there was a .005 taper and I stated more uniform force, not perfect! It is just a suggestion like many others here and perhaps a new way to look at it. There are other avenues of approach to help on clamping without redesigning the wheel.

I don't think there is a need to get into the minutia of things for someone else's product with such limited information that has been provided!

 

[eKretz]

What do you mean VARIANCE? It said it was tapered

What do you mean by VARIANCE, microns, thousandths, inches, feet, miles? The OP stated that there was a .005 taper and I stated more uniform force, not perfect! It is just a suggestion like many others here and perhaps a new way to look at it. There are other avenues of approach to help on clamping without redesigning the wheel.

I don't think there is a need to get into the minutia of things for someone else's product with such limited information that has been provided!

First off, calm yourself down. What I meant was that he is obviously planning to produce these parts for sale as an accessory that mounts to some existing product. If that product does not have the same taper uniformly in all of its parts, then your suggested solution will not be of much use. What if the next one has .005" taper in the opposite direction? Then your solution will only clamp at the big end. He did mention varying tapers and that some parts might be straight. Maybe slow your roll and take a little more time to comprehend what he wrote.

A better solution might be to split that long side up so that you have a couple of sort of narrow flexible strap clamps and two separate clamping screws, one for each. That should solve the problem completely and also allow for a variance in tapers between parts with no issues. I'm assuming that the issue is at the long side. Pardon the crappy 10 second photo sketch.

 

[rons]

The sand paper idea will work. But over time the sliding will screw up the finish on the shaft. I would not use sand paper.

 

[rcoope]

I seem to find myself making rod clamps or teaching engineering trainees how to make rod clamps quite often. And there are numerous such clamps on bicycles such as the stem, seat post collar and brakes and shifter mounts which we're always faffing about with. Your best bet is definitely to have an accurate match between the collar and shaft. This seems to result in exponentially more clamping force and it doesn't much matter if one or the other surfaces is anodized. Based on that, it would be tempting to match the taper in the clamp. The problem I'd see is the clamp then has to be axially constrained to grab the taper in approximately the right place as the farther towards the taper end it moves, the less clamping force there'll be.
Another thought is, if this was a production product, to mould a two part plastic taper adapter that fits inside the aluminum clamp. That would be a bit like that common wire rack shelving system with the tubular uprights with periodic grooves. The shelves have tapered tubes at the corners that drop down on plastic adapters that squeeze the uprights, using the grooves for initial location so all the corners can be set to the same height. The plastic sleeves are tapered on the outside and straight on the inside whereas you'd have the opposite.

 

[helmbelly]

Great thoughts people. I've been carefully reading your replies and it's smart stuff. thanks. I was sick for a couple days - sorry for late follow up.

I have two clamps in this part 1. is the upper and lower jaw clamp that closes north to south in the photo with two screws- that's the one that's being the worst pain pairing to another pre-existing tapered part out "in the world" and I'm still researching how much they vary. 2. is the slit clamp- a plunge bore, a slit and a bolt. That's working ok bc I control the rod that is clamped there. But I'm not happy with it and your ideas are - well about to get tested on the mill this week.

I seem to find myself making rod clamps or teaching engineering trainees how to make rod clamps quite often. And there are numerous such clamps on bicycles such as the stem, seat post collar and brakes and shifter mounts which we're always faffing about with. Your best bet is definitely to have an accurate match between the collar and shaft. This seems to result in exponentially more clamping force and it doesn't much matter if one or the other surfaces is anodized.

12 years ago a machinist friend made both a slit clamp and a jaw clamp- both grabbed a 15mm camera "iris rod" of 6061 anodized tube. They both clamped great. Later I started machining my own stuff -mostly Delrin but those clamps held tight too. Like zero slip. Now that I'm having trouble and just thinking about some replies here I'm starting to suspect with the slit clamp maybe there is too much rigidity behind the bore, maybe I'm leaving too much meat on the binding of the bore, if you were looking down on a book it would be the thickness of the book binding the metal that connects the front and back "covers".

I fished a part my machinist friend made and his binding is .085. The ones I'm making are .125. I think I need to try his dimension on the slit clamp.

Based on that, it would be tempting to match the taper in the clamp. The problem I'd see is the clamp then has to be axially constrained to grab the taper in approximately the right place as the farther towards the taper end it moves, the less clamping force there'll be.

I don't quite follow "axial constrained" I get that the taper match is needed.

Another thought is, if this was a production product, to mould a two part plastic taper adapter that fits inside the aluminum clamp. That would be a bit like that common wire rack shelving system with the tubular uprights with periodic grooves. The shelves have tapered tubes at the corners that drop down on plastic adapters that squeeze the uprights, using the grooves for initial location so all the corners can be set to the same height. The plastic sleeves are tapered on the outside and straight on the inside whereas you'd have the opposite.

Yeah this where my head has been the whole time. I'm thinking with my vise I put a piece of alum or copper wire to take up lack of square for a part I'm workholding. Why not have a shim instead of cutting a taper which is still a question mark/research project. Even if I had to cut an inside groove and set it with a hammer. I mean for testing if I'm dealing with .005 over an inch I should try wrapping the thin end of that inch in some cigarette paper as was suggested and see. I mean I could literally find some thin durable adhesive tape that might make that taper parallel. But for .005 over an inch is there a tapered bit ? It just seems like awful little to worry about !

 

[helmbelly]

The sand paper idea will work. But over time the sliding will screw up the finish on the shaft. I would not use sand paper.

yeah I have tried roughing up surfaces in the past and it didn't work right, I can't recall why, but I stopped doing it. I did not clamp on actual sandpaper tho

 

[helmbelly]

A better solution might be to split that long side up so that you have a couple of sort of narrow flexible strap clamps and two separate clamping screws, one for each. That should solve the problem completely and also allow for a variance in tapers between parts with no issues. I'm assuming that the issue is at the long side. Pardon the crappy 10 second photo sketch.

View attachment 373801

This is brilliant, I dont think I ever would have come up with this approach.