Dust fittings, of a sort

Jim Murphy · 02-11-2008, 12:29 PM

Okay, okay, I know you're growing weary of all my duct-dust threads, but I just had to share this.

Getting plastic flex over the S&D pipe is a frustrating challenge. I tried the freezer and hair dryer trick (didn't work well), liquid dish detergent (works great slipping the pipe into the fittings and allowing the fitting to swivel to fit, but sucks trying to get flex over the pipe). So what the heck, I tried making a reducer.

If you look carefully, you can see the seam in the smaller diameter pipe. I sliced out a section lengthwise on my cheapo B&D 3 wheel bandsaw, sanded the edges with 220, applied a liberal amount of PVC cement to the seam (inside and out) and then around the perimeter, and slipped the section in the standard pipe. I wouldn't use this for a pressure fluid application, but for dust work, it works real well. Feeding the pipe slowly into the blade is helpful.

Now, I know you hate math, but it can be your friend. The wall thickness of my 4" D2729 pipe is 0.085" (for the 6" stuff, it's 0.11~ or thereabouts). By doubling the wall thickness, and muliplying by that nefarious constant Pi (3.14159), we derive the value of 0.53". Mark that width on the outside of the pipe, slice it out, and glue it up. The plastic flex slips easily over the reducer.

If I had thought to do this before I bought my expensive acrylic tubing, I would have had enough pocket $$ to buy something worthwhile.

FredP · 02-11-2008, 12:41 PM

these are what Im using.
http://woodcraft.com/family.aspx?familyid=3947
the flex screws on one end and the other end fits perfectly inside S&D fittings. I used PVC glue to attach to the pipe fittings and it works good.

fred

Bas · 02-11-2008, 12:44 PM

Now that is a great solution. Given that the PVC cement pretty much fuses the pipe back together, I think it's an extremely strong joint, especially since it's inside another pipe.

Cuprousworks · 02-11-2008, 01:51 PM

Nice solution. Of course, now that I know how the cheapskate in me will insist on making my transitions from scrap instead of paying $4.50 per...

Funny thing, my first reaction was "that's pretty thin walled stuff - can it really be 1/2" difference in the circumference between inside and outside walls?".

You're right, of course. Almost any calculation with circles is hard to estimate: would you have guessed that the total area would be constricted by 1 inch for this modification? That's a 8% reduction in area! (more fun with your friend, pi, if my memory of geometry is right)

Mike

scsmith42 · 02-11-2008, 01:55 PM

Jim, that's a neat idea!

Scott

MikeL · 02-11-2008, 02:15 PM

That is a fantastic idea Jim. I was looking at the threaded adaptors this weekend. Right on time.

McRabbet · 02-11-2008, 03:24 PM

Ironically, three years ago when I built this Chip Separator

from plans in ShopNotes (No. 55, IIRC), they showed how to make adapters for the 4" flex entering and exiting the top of the unit by taking a slice out of a piece of Schedule 40 PVC as you described and then cutting kerfs with your bandsaw on the inside of the pipe every 1/2" or so to allow it to be more bendable when closing the gap.

There is a neat trick they explained in how to calculate the size of the cut you must remove to reduce the pipe size with no math involved. Use a strip of copy paper and make a "hoop" with it to fit inside your flex. Mark the point of overlap on the inside of the hoop. Then wrap the paper around the larger pipe and the cutout is the difference between the mark and where the end intersects the wrapped end. Works for any size as long as the paper strip is long enough.

PurpleThumb · 02-11-2008, 03:50 PM

Originally Posted by FredP

these are what Im using.
http://woodcraft.com/family.aspx?familyid=3947
the flex screws on one end and the other end fits perfectly inside S&D fittings. I used PVC glue to attach to the pipe fittings and it works good.

fred

I used the same system, Fred. Work extremely well and have the added advantage of being able to take them apart if needed.

Alan in Little Washington · 02-11-2008, 06:14 PM

Originally Posted by PurpleThumb

I used the same system, Fred. Work extremely well and have the added advantage of being able to take them apart if needed.

You need to be careful- the threads on some flex are backwards from those fittings.

McRabbet · 02-11-2008, 07:15 PM

Originally Posted by Alan in Little Washington

You need to be careful- the threads on some flex are backwards from those fittings.

And you won't find them for 6" flex, either!

erasmussen · 02-11-2008, 08:19 PM

Looks like a good fix

Gotcha6 · 02-11-2008, 09:42 PM

Glad to see a solution so simple. This stuff don't hafta be rocket surgery or brain science. Keepin' it in mind....

Travis Porter · 02-11-2008, 11:56 PM

Originally Posted by fernhollowman

If I had thought to do this before I bought my expensive acrylic tubing, I would have had enough pocket $$ to buy something worthwhile.

Was this one of those

moments? I seem to have them frequently myself.

Jim Murphy · 02-12-2008, 10:20 AM

Originally Posted by Travis Porter

Was this one of those moments? I seem to have them frequently myself.

Yep. Without doubt, IMO, the most perceptive and salient tag line on this board belongs to Bas.

His axiomatic aphorism relating to experience and when it is gained is profound beyond words.

tip o' the hat

to Bas.

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