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Unread 10-06-2017, 07:11 PM
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ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$tools

OK all of you tricky machinists... I've got one for you... I work mainly with startup teams, that don't have big shops yet. AND, I'm working on yet another of my infamous "Hardware Store Hack" (HSH) projects...

NEED: Advice for a SIMPLE, CHEAP way to open up the ID of a LONG (over 1 foot) section of basic 3/4" PVC pipe, up to around 7/8", so it can slide over your basic off-the-shelf 1/2" black/galvanized pipe (~0.875" OD, Galvanized's OD is a few thou smaller than black pipe). Preferably, without using a lathe (which is not often available yet to most startup teams).

(It's A Long Story as to WHY... I'm not discussing the project itself until I know if it'll work, so please don't argue WHAT and WHY here. I just need a HOW for now...)

BTW... The "HSH Series" Goal: New teams often have little money and no shop (let alone advanced machines like mills, lathes, 3D printers, etc). So they need to make useful widgets for their bot for VERY cheap, using mainly hacked hardware store and recycle/reuse items, readily available-in-any-community cheap materials, and simple hand and hand/power tools. Those kind of projects are what I'm creating.

THIS project's challenge: Everything else (so far) has been hardware store off-the-shelf. It's this darn PVC that's the challenge, because even if you have a mill or lathe (or that expensive 7/8" reduced shaft drill bit) its the DEPTH that's making it difficult. Due to length, simply coming in from both ends with a 7/8" bit may NOT be sufficient. Worse, I don't see the old style "2 set screw round extension bars" available locally any more. Most small town stores (and big box stores) now only carry 1/4" HEX extension bars, for power drills, and rarely have 1/4 round, let alone extensions for the 1/2" shaft that most 7/8" reduced shank bits use.

Thoughts:

IF I were to use a lathe: The obvious choice for me is to just use the lathe to whip up a custom extension rod, that'll accept the 7/8" bits that I can find. I'd drill the end of a nice long slice of thick round or hex shaft to accept the reduced shank drill bit, add two setscrews to the side, and plug in an off the shelf step drill bit (ie the 7/8" max HF #96275 step drill...). If need be, turn a round on the other end of the hex rod for a standard smaller drill chuck (or adapt a 1/4" hex drive end to it). Easy Peasy... But that requires a LATHE, and many startup teams don't have one yet to replicate my instructions, which violates "HSH guidelines".

BTW... The HF website LIES... The 96275 shafts are 3/8" (actually 0.370") round with a flat, NOT 1/4" Hex! Had the latter been true, I'd could have done the whole thing with off the shelf parts!

The best ideas I've had so far are:

1) Create a 3/8" shaft coupler by drilling out a hardware store hex shaped threaded coupler to the needed size, and drill/tapping a pair of setscrews into its side... If necessary, file/grind add a pair of flats onto the two coupled pieces for better setscrew traction. Awkward, but it can be done with a hand drill and hand tools. The initially threaded center eliminates the need for a lathe, and the resulting adapter allows you to couple on a simple matching diameter solid rod as an extension to the above readily available HF bit. I'm not sure how long of a coupler I can find at the store (for stability), and how that bit will track, but I'm hoping the Step in the bit will help keep it centered as it travels down the pipe.

2) (and I haven't TRIED this yet!) Perhaps create a "centering guide leader" out of a simple wooden dowel, fitted to the original PVC's ID?

Idea: Given a dowel that matches the original ID, center drill & slit one end, bury a cheap long shaft 7/8" flat wood bit into that end, and side drill&screw it through the spade flat to form it into one solid assembly. Wax the dowel. You now have a leading dowel, with two "L-spurs" projecting from it, driven from the other end by a 1/4" hex drive.

In THEORY:Clamping the PVC pipe, the long wooden dowel now "center guides" the readily available inexpensive long shaft 1/4" hex driven 2-blade spade bit cutter down its length with a cordless drill, and off the shelf 1/4" hex drive extension rods. Sure, it'll have to be all done in one pass, and may have to be backed out a lot to clear chips (tapering the leading edge of the dowel helps re-entry), but this MAY work. It's also cheap, ALL tooling parts should be readily available locally, and is inherently self-centering so I shouldn't have to worry about drift.

I'm hoping the PVC is soft enough that a "stabilized wood spade bit" will work... (Yet TBD...)

Some of my Bad Ideas, considered and rejected:

3) Find a drill-drum sander with a 1/4" hex shaft that can be extended with the off-the-shelf extension, jig it, and make lots of dust (ick, and hard to center it...) If I could center the drum's parts onto a long threaded rod with lock nuts on either side, it MAY work by being supported at both ends, but it's still "ick" in my book...

4) Extend a round or half-moon file somehow, and waste a lot of time (also ick...)

5) A Dremel solution? Most Dremel tools are too fat for the pipe, and flexi-extensions need to be managed.

6) Use heat? IE using 7/8" dia "melt slugs", or recasting it to the right spec all involve very bad, dangerous fumes, forms, and the swarf may pile up, plug and/or melt the pipe's sidewalls! (very ick, and I'm not suggesting this to newbies...).

7) Welding on an extension rod? (Alignment issues, and not many new teams have welding available...)

Anyway... There's GOT to be a simple way for newbies to do the PVC pipe open-up mod operation, without requiring a lathe and/or expensive tooling.

So far, #1 and #2 (or some combination of them) are my best ideas, both yet to explore.

Your thoughts, oh Great Machinist Gods out there? How do I do this, without a lathe? Will #2 even work, or did I miss something with it?

Thanks!
- Keith Mc.
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Last edited by kmcclary : 10-06-2017 at 08:03 PM. Reason: Added data
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Unread 10-06-2017, 07:20 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Silly little idea... What about figuring out a way to embed a razor blade in a dowel of the right size, effectively creating a circular plane? You'd need a leading AND a trailing dowel of the proper size, but it should work. (Could even use the next size down of PVC?)
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Unread 10-06-2017, 07:27 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

#2 is a thing I've seen them sold commerically years ago, but you probably can't find them anymore. The one I saw was sold for enlarging the hole in doors for the latches.
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Unread 10-06-2017, 08:12 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

A brake cylinder hone should work. You'll probably need an extension but they come with a flexy shaft anyway so it shouldn't be too difficult.
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Unread 10-06-2017, 08:48 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Try looking for PVC-120 3/4" "flex pipe" PVC. I bought some at the Menards chain years ago. I think it is an irrigation product. I have a piece I measured at ~0.910" .. the web site below shows I.D.s they list at .786" and .850".

https://flexpvc.com/cart/agora.cgi?p..._Pipe_3/4_inch

I used it for network conduit thru a non crawlable crawl space. I wiggled it into place and used a shop vac to suck up the pull string.
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Unread 10-06-2017, 09:50 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

PVC pipe softens very nicely without burning or fumes if you heat it SLOWLY with a heat gun. I would make a mandrel out of a wooden dowel, tapered so you can push it into the softened end of the pipe easily. Put it in some kind of alignment jig - v blocks, maybe - to hold the two sides co-axial, then let it cool, extract the mandrel, and insert the pipe. I have done this.
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Unread 10-06-2017, 10:04 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

yup, heat was the first thing I thought of
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Unread 10-07-2017, 12:15 AM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

I'm thinking a 7/8 inch plunge router bit and a long 1/4 inch metal shaft would do the job. Couple the bit and shaft with a simple 1/4 inch shaft coupler and drive it with a drill.

You could use some 1/4 ID 7/8 OD Fender Washers to keep it centered if needed.
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Unread 10-07-2017, 06:21 AM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Does it have to be PVC? you could buy a plastic tube with a 7/8" ID.
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Unread 10-07-2017, 06:39 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Quote:
Originally Posted by EricH View Post
Silly little idea... What about figuring out a way to embed a razor blade in a dowel of the right size, effectively creating a circular plane? You'd need a leading AND a trailing dowel of the proper size, but it should work. (Could even use the next size down of PVC?)
Funny you should mention that one! On PBS's "The Woodwright's Shop" they recently had a DIY wood reamer like that. It crossed my mind just after I submitted the original post. (The post was too long already.) I'd have to make a dual sized plug (before and after), with the cutter in the middle. A good idea, but without using a lathe to get the two diameters right it may be a challenge {for the newbies} to fab.

Quote:
Originally Posted by Mr V View Post
#2 is a thing I've seen them sold commerically years ago, but you probably can't find them anymore. The one I saw was sold for enlarging the hole in doors for the latches.
Cool.. That was off the top-o-head. Remember its "official name"?

Quote:
Originally Posted by mman1506 View Post
A brake cylinder hone should work. You'll probably need an extension but they come with a flexy shaft anyway so it shouldn't be too difficult.
Hmmm... Not sure that's the right tool. Brake hones are stones, best for "fine surface finishing of metal", and small removals. This will require a good 1/8" overall of PVC to be removed, over a long length.

Quote:
Originally Posted by Tom469 View Post
Try looking for PVC-120 3/4" "flex pipe" PVC. I bought some at the Menards chain years ago. I think it is an irrigation product. I have a piece I measured at ~0.910" .. the web site below shows I.D.s they list at .786" and .850" {...}
Interesting! I only need a couple of feet. Your link shows big rolls. Is is sold by the foot at Menards? The informal HSH guidelines call for it to be "available in almost any small town". I'll have to see how "common" it is. Thanks!

Quote:
Originally Posted by buchanan View Post
PVC pipe softens very nicely without burning or fumes if you heat it SLOWLY with a heat gun. I would make a mandrel out of a wooden dowel, tapered so you can push it into the softened end of the pipe easily. Put it in some kind of alignment jig - v blocks, maybe - to hold the two sides co-axial, then let it cool, extract the mandrel, and insert the pipe. I have done this.
FYI, another piece perfectly slides over the OD as is, so I wish to open the ID without distorting the pipe's OD. I'm afraid plastic deforming the pipe would add more problems later.

Quote:
Originally Posted by InFlight View Post
I'm thinking a 7/8 inch plunge router bit and a long 1/4 inch metal shaft would do the job. Couple the bit and shaft with a simple 1/4 inch shaft coupler and drive it with a drill. You could use some 1/4 ID 7/8 OD Fender Washers to keep it centered if needed.
Hmm... I'm unsure that would keep the hole from drifting to failure. You need to guide the leading edge, not the trailing edge. Washers behind could easily follow the new hole out the side.

{adding in one more}
Quote:
Originally Posted by Gdeaver View Post
Does it have to be PVC? you could buy a plastic tube with a 7/8" ID.
Well, not necessarily, but I chose 3/4" PVC because it's not only cheap, it has the perfect OD for this job, AND it accepts other cheap parts on its surface.

I'm creating a stacked assembly, out of compatible, cheap parts. I can change the overall scale, but fitting tolerances between parts do matter. As there's stuff both on the inside and outside of the PVC pipe, and I also need to add some compatible coupling parts to the ends, then if I were to replace it with something else lots of other dominoes fall.

So, I'm right back to simply fixing the ID of this ONE part. As PVC is pretty soft, I just thought there would be a lot of cheap options to adjust its ID size a tiny bit.

{/add in}

Great ideas... Please keep them coming!
- Keith
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Last edited by kmcclary : 10-07-2017 at 07:49 PM. Reason: An additional reply..
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Unread 10-07-2017, 06:59 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Adjustable reamer?
We have some like these, but you'd want one in the size you are looking for.
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Unread 10-07-2017, 07:14 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Grind a slight taper on the corners of a 7/8" paddle bit. Then you can use the 1/4" hex extender to make it long enough.

If I look, I can probably find the bit that I ground like that, although I forget what it was for.
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Unread 10-07-2017, 08:04 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Honestly, if I really needed plastic pipe with a 7/8" OD and no access to advanced shop tools, I'd just buy #8585K202 from McMaster-Carr. This would cost like $10 over what a regular length of 8-10 foot length of 3/4" PVC pipe would cost, but would be significantly safer and faster than trying to cobble together a tool to ream out a foot+ depth of PVC pipe.

But if we're stuck in some random barn and need to MacGyver our way out, with the key to freedom being to increase the ID of 3/4" Schedule 40 PVC Pipe from ~0.82" to 0.875" along the entire length of the pipe, with only access to basic tools and home improvement store raw materials, I'd probably try a some variant of #2 (spade drill with wooden dowel plug to guide it along existing PVC pipe ID, and some kind of fabri-cobbled drill bit shank extension). My biggest concerns with this approach would be the drill bit shank extension causing excessive speed wobbles and chatter, and the dowel plug not being sufficient at preventing the drill bit from hunting around the ID and busting through the side wall of the pipe (could likely be made worse because the PVC pipe is sagging and not straight).
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Unread 10-07-2017, 08:39 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

Another consideration is how tight the size tolerances are on your materials. If you buy common materials from one source, and expect them to be the same size (within a few thousandths of an inch) as similar materials that others purchase from another source, you might have problems..

anyways...did you look into using Schedule 20 PVC pipe?
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Unread 10-07-2017, 11:58 PM
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Re: ShopTricks - How to enlarge a 3/4" PVC Pipe's ID to 7/8", without a lathe or $$to

I wonder if there exists any step drill (unibit) that maxes out at the size you want, and has a 1/4" hex shank.
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