Tubular Slippage: Fluted Knob Not Clamping

December 5, 2014 4:36 PM

This drafting table I acquired second hand is not staying put. The clamping knobs are tightened as tight as can be, but the table surface still sags. If I set the surface level, the clamps slip almost immediately and the surface drops to its lowest position. Is there a way to fix this?

I don't know if I am explaining myself well because I don't know the terminology for this mechanism. The bolt end of the knob is not clamping the interior tube. I've tried to google everything I could think of like set screw lag bolt fluted hand knob pipe slippage tubular clamp sag to no good end.

posted by at the crossroads to Media & Arts (11 answers total)

You might try layering tape inside the gripping surface to reduce the diameter, and increase the effectiveness of the gripping surface in relation to the screw tightening.
posted by nickggully at 4:45 PM on December 5, 2014

Sounds like either they have the wrong bolts or the plastic collar is just stretched too far to clamp effectively anymore, which we really can't tell without some good pictures of what's failing.

Barring that sort evidence-based of failure analysis, if this were mine, I'd probably look into finding an alternative clamp, like a cheap set of alloy quick release bicycle seat post clamps, to fit the diameter of the upper/inner tube. Those are plentiful and cheap, but that's only a viable options if a) the diameter of the inner tubes are within the clamping range of an existing seat clamp, and b) you don't need to prevent the surface from rising, just form falling below whatever height you set it to.

If you can't use a seat clamp, well, McMaster.com has various collars and clamps, but you will pay a lot more for them. So, hopefully this tube is in a seat-post friendly size.
posted by mosk at 5:00 PM on December 5, 2014

Response by poster: Yes, mosk, thanks. It is similar to a bike seat post clamp.
I'm still at a loss for what to google because I don't know what to call it.
Knob and Collar clamp? telescoping post ...??? Surely there is a name for this type of design?
posted by at the crossroads at 5:10 PM on December 5, 2014

Well, it looks to be a two-step collar clamp -- the inner step is a bit narrower to clamp onto the inner/top tube, while the lower portion of the clamp is a bit larger, etc. If you know the manufacturer of the table, you can write them and see if they can sell you some replacements. Or, if you really want us to help you troubleshoot the existing clamp, it would be very helpful to see some clear pictures of the way it is failing. I get what you are saying, but some closeup pictures of it at "full clamp" would be better.

That said, I hate plastic for this sort of thing. If it were mine, I'd dig up a caliper and take an exact measurement of the diameter of the inner/top tube, and see if you I could simply replace the plastic clamp with one of the aforementioned bicycle seat tube clamps. Alloy trumps plastic for this sort of thing, and maybe you'll get lucky and it will be a standard size. Clamping on the top tube alone won't prevent the table from rising, but if your weight is on it as you work that shouldn't be an issue, as you really only need to keep it from sliding downwards.
posted by mosk at 5:19 PM on December 5, 2014

Oh, and I think a good search term is "adjustable pole clamps". That will get you down the right path, anyway.
posted by mosk at 5:30 PM on December 5, 2014

As a temporary fix, you could cut some cardboard rectangles and slip them between the inner and outer posts. Should hold for a while unless the collars have stretched out.
posted by Johnny Wallflower at 5:41 PM on December 5, 2014

Easy-peasy fix -- go to an auto parts joint, get some hose clamps of appropriate size, attach them where you'd like them, problem gone. It's tacky of course, but you can appease your inner need to be cool by calling it "steampunk" or some such, tell your friends you did it for the funky look.
posted by dancestoblue at 6:21 PM on December 5, 2014 [1 favorite]

Alternately, if you're at all handy and have a drill, you could get it where you want it and then run a self-tapping screw into it; problem *definitely* fixed then. (Self-tapping means that the screw has a point that is like a drill bit, cuts its own hole, you don't have to pre-drill, you can buy a few of them at Home Despot, if you live in Austin I'll give you some, hell, I'll fix the thing, you'll have to supply a cup of coffee is all.)
posted by dancestoblue at 6:25 PM on December 5, 2014

Cut a strip of beer can and use it to shim inside each clamp.
posted by notsnot at 6:58 PM on December 5, 2014 [1 favorite]

That is a cheap but functional table and I sold many.

Call Alvin. They are kind of rude by my standards, but they will send you parts and take the time to understand what the problem is. They care about their name.
posted by Mr. Yuck at 8:07 PM on December 5, 2014 [1 favorite]

The Onyx is designed to fold for storage, so the more permanent suggestions here may not be quite what you're looking for. As a quick (but temporary, depending on how often you adjust the height) fix, you can loosen the clamps and pull the top completely out. Loosen the clamp screw until it's floppy-loose, and then run a ring of 2" wide masking tape around the inside of the clamp, on each leg. One layer should do it. Re-install the top half of the table and test. May need to go to a second layer of tape. It'll hold, but if you adjust the table up and down a lot, it'll wear the tape down pretty quickly. Do not use skateboard tape unless you want your painted table legs to get all scratched up.

Seconding Mr. Yuck; we also sell Alvin tables, and I've seen this very symptom before. The plastic clamps stretch and they will no longer hold tight. You can certainly call Alvin; they'll sell parts to end users. [phone] or [e-mail]. They are indeed a little brisk on the phone, but be persistent and you'll get results. The Onyx table is still current product, so they should be able to help you out.
posted by xedrik at 7:54 AM on December 6, 2014 [1 favorite]