Square plastic tube plug model?

I need exact dimensions on a cap/plug for square aluminum tubing, and I
can't seem to find data anywhere on the Net. The best I can do is stuff
like is shown at the following URL (and also on McMaster-Carr's site)
but I doubt if the "SQ 8-1" Niagra Plastics part specified on this Web
page will fit properly. The experience I've had with these ribbed plugs
is that they actually fit a much narrower range of wall thicknesses than
they say they do, and my application will be up near the upper end of
the thickness range this part is supposed to fit. Highly likely NOT to
fit at all without using a sledge to put it in, and even then it'll
probably pop out.

http://www.niagaraplastics.com/prodfurnguide.asp?site=squa_sq.htm

I'd rather use something like what I can find in McMaster-Carr, but they
don't give enough dimensional data to be useful and there's no CAD model
available from them. I've looked at Caplugs, Mocap, Heyco, Stock Caps,
etc. without finding anything worth looking at. Of course I've done
Google searches based on all kinds of combinations of keywords. I've
got a 1" aluminum tube with a 1/8" wall thickness. Anyone know where I
can get data, or (better yet) a model?

TIA
Mark 'Sporky' Stapleton
Charlotte, NC

 

Spork,

At Heyco UK, you can get some details on the 25mm square hole plugs.
http://www.heyco.co.uk/products/default.asp?group=CAA

...

 

If you want to buy these kind of parts, you might check with Rodon, in
Hatfield PA, I believe, and also National Molding Corporation, in Long
Island NY. You should be able to find their websites via their names.
They both have some kind of items similar to this.

 

If you want to design your own, just make the fins to taper out to be
very thin at the ends, and allow some interference to keep the plug in.
Allow .10 or so at the end before the first fin to make it easy to start
in the tube. Leave thick ribs under the head so that the cap can't move
sideways after it is inserted.

 

One more thing: it would be good to get a prototype tool made if
possible, so that you can adjust the parts to get the pull-out force
that you need before you commit to a lot of cavities in a real tool.

 

Those guys at 8020.net who sell the extrusion components have plain square
tubing, perhaps they have suitable plug dims.

Nyuk Nyuk Nyuk

 

Thank you, sir (and also thanks to Paul S.). I found the kind of part
I'm looking for on Rodon's site, although once again as with
McMaster-Carr there's no useful dimensional data. Can't find National
Molding in Long Island at all, even though I found an article
referencing their CEO. I guess I'll just "fake it" for now.
Regardless, I doubt if we want to be creating a custom part.

Of course if I DID want to get a custom part made I would take your
advice and create a rapid prototype. In case anyone has the need I've
been getting automatic quotes from Quickparts.com for durable SLS parts
that really blow me away. Fast, cheap AND good -- that's amazing. Ya
send 'em STL files and the quote comes back in about 15 seconds. It's
obvious that the quote machine takes into consideration that they can
create multiple parts on the table at one time, and they discount
accordingly because of the machine time saved. Among other things, ya
can get nylon and glass-filled nylon and ABS models made CHEAPLY. Parts
are made in 2 to 3 days and shipped standard overnight for the quoted
cost. Damn! These people have it down to a fine science.

Mark 'Sporky' Stapleton
Charlotte, NC

 

Browse this site Mark. Might be able to help. http://www.solusii.com/
Jimmy
Mt. Olive, NC

 

Thanks also Devon and 3 Stooges. I hadn't thought of 8020. From what I
found so far there it looks like the end caps they have are intended for
their standard structural extrusions, not simple square tubing, but I'll
look at some other similar sites. Can't afford to use the typical kinds
of extrusions sold by 8020 or Item or Bosch, etc., not only from a cost
standpoint, but also from a weight standpoint. I'm working on a cheap
consumer product, not a machine structure. Appreciate your time and
thought regardless.

'Sporky'

 

Interesting site, regardless, Jimmy. Thanks. I'll bookmark this one,
as I often get into machine design and such.

'Sporky'

 

So.. looking again,.. wouldn't the SQR-1-10-14 from Caplugs work?

http://www.caplugs.com/images/CAD/vc_SQR.pdf

...

 

GREAT, Paul. I had looked through Caplugs twice (the 2nd time on your
recommendation) and didn't find that. But no, unfortunately I don't
believe the parts listed there will work. I've got a 1/8" wall on the
tubing I'm using -- quite on purpose. I need to form some threads
through one side of the tubing, and 1/16" just isn't enough thread depth
for the application. Thus the inside square dimension in the tubing is
..75 and the smallest rib dimension on the plugs intended for 1" tubing
is .871. Appreciate very much your checking it out for me though. As
always you're a gentleman.

'Sporky'

 

FWIW, my experience with these types of plugs has convinced me that any
more than some nominal interference fit doesn't work well at all. The
interference with the part you (Paul) pointed out is almost 1/16" on a
side and that much almost certainly will be a PIB at best. Half that
much interference fit might work pretty well. The companies that sell
these things (like Caplugs) often greatly exaggerate the range of
internal dimensions their parts will fit with, and I suspect that's so
they don't have to have as many molds and stock as many different sizes.

Marky 'Sporky' Stapleton

 

Here is where we get all of our plugs. It seems to me that the finned caps
do seem to work with many wall thicknesses, but these guys will send you
free samples of most items like that.

http://www.outwater.com/

 

Wow, now that site has a lot of different & unique *stuff* on it. I'll
bookmark that one for later use as well. Thanks for that link, Devon.

'Sporky'

 

Sporky,

You say you need to thread one wall, and this is the reason for going with
the thicker wall tube. Have you considered flowdrilling?
http://www.flowdrill.com/technology.htm

We do a lot of this at my company when we need to attach something to
thin-wall tube. Basically it's friction-drilling. It uses a special
"drill-bit" in any standard commercial grade drill press (hand drills won't
work), and deforms the material of the hole instead of cutting it. What you
have after drilling the hole is cone of material that is draw down into the
hole, which creates enough material thickness to allow you to thread more
material than the what you started with. We've been flowdrilling at my
comapny for a few years now, with little problem. We usually use HPRO & CRS
1020 tubing, as well as AISI 304 without any trouble.

It's just something to consider if you are having trouble finding the proper
caps you are looking for.

Ray
Los Angeles, CA

 

Now THAT's a nice machining process to know about regardless. Makes ya
wonder whether the melted area becomes annealed in many instances,
however, which of course would reduce the thread strength possibly even
to a severe extent. I imagine that is addressed somehow, but it's not
clear how. Unfortunately I can't use it 'cause I can't afford a boss on
the outside, although one inside would be fine. I'll remember it,
though. Thanks for the link, Ray. Learn sumpin' new every day!!

'Sporky'

 

You can get a flowdrill that does not leave a boss on the OD of the tube
being drilled.
http://www.flowdrill.com/manual.htm

Either way, good luck on your hunt for a cap plug.

 

The issue of the boss on the outside is a function of the speed, timing &
plunge. I have a sample that I got at IMTS that shows both ways. When I
watched the process, it was easier to visualize how it all works together.

WT