How to bend 7/8 tube for new seat platform.

Hi all, Fred out of the Big Valley California. I am new and looking for help. My first build was in 1974. Now some years later need something to do. So I bought me a xs650 and away I go. To keep my cost down, I will fabricate and tack weld myself. I have a friend who can complete the welding. I want to go from (photo1) this. To this you see in (photo 2)

So my question is, has anyone of you done something like this and a cheap tool to do it with? I will use the tool only once for this project.

Welcome back to the '70s, oldspice.

There's a lot of threads, found by typing "tube bender" in the google custom search.

I recall some folks using wood forms, but that may have been for aluminum, and I can't find those threads.

Years ago, I was able to get some tube and pipe bent at a muffler shop that had a hydraulic bender with numerous dies...

Hi 2M, thanks for the come back. I have been checking the resources you mentioned. A lot out there. My bike is a 78 and has been hack up pretty good by the previous owner. But I will get it right. Going to make it right for my grandson.
Thanks Again!

Hi Fred and welcome,
whaddya mean, "only once" ? Wanna bet?
OK, 7/8" mechanical tubing is thick walled enough, I'm guessing it's 11gauge,
to make easy bends in without being packed with sand or filled with cerrobend.
The least costly way to bend such a tube is to torch it red hot and then bend it over a wooden form.
Yes, the form will certainly scorch and may well catch on fire. That's what the bucket of water is for.

Hi Fred, Fred here. Getting a little confused yet - LoL. Nice to hear that name. Yea you are probably right about the using once. Good info, now how to get the form right. I am looking on Craigslist for a cheap bending machine or even Harbor Freight. Just finished up rebuilding the front end, new neck bearing and shaved the forks. Polished out real nice.

Hey all this bike stuff almost makes me feel like I am in my mid 20s again. Loving It!

Hi Fred,
perhaps an electrician's conduit bender would work?
I know they are meant for lighter wall tubing but perhaps it'd stand up to limited use?
It's amazing what you can find in pawnshops, too.
My son found a quite nice radial arm saw for less than 1/2 price in his local pawnshop.
Didja replace the neck bearings with tapered rollers?
Hope you left at least one set of brake caliper lugs on the forks when you shaved them.

Hey Fred, yes to the bearings and lugs. One of my hobbies is garage sales and fleamarket. Never thought of pawnshops.

A steel tube furniture maker should be able to bend the hoop for you. Draw up the bend you want (actual size) on cardboard to use as a template. This is only viable if you have a furniture manufacturer in your area.
Steel tube benders capable of bending that size tube are expensive, even the used ones.

Well , thank you all. We're there is a will there is a is a way. When I come up with a idea on how to do it I will post it here.

Hi,

Instead of doing this yourself, you may want to consider contacting a race car, kit car or performance go-cart or off road vehicle manufacturer. It will probably be cheaper for you in the long run. You could figure out what you need for bend radii and weld the bends to straights as another option.

If you want to do it yourself, then the comments about filling the tube with compacted fine sane or cerrobend. You will then need a form or mandrel that goes about halfway around the pipe to prevent kinking of the tubing. Mention was made about heating the tube. Filling the tube would still be required and make sure you don't quench the tubing in water, only the wood form! A bucket quench will make the tubing brittle and that is the last thing you want for the frame.

I re-purposed a Harbor Freight pipe bender to bend tubing for part of a sidecar frame I built. I made a sheet metal shoe to go between the mandrel and the tubing being bent to compensate for pipe to tube OD dimensions. I've attached a couple of pics showing this. I filled with fine "play sand" I got at Home depot or Lowes. the tube had an 1/8" thick wall.

Thicker wall tubing will be less likely to kink than thin wall but requires more force to bend. An electric conduit bender will work on only thin wall. When you bend, if using longitudinal seam welded pipe or tube, make sure the weld is on the neutral axis like my picture, i.e. in the middle of the bend when looked at from the side. The tube below this line is in compression and above in tension. Bending always tries to go oval or kink the pipe or tube and that is why you need filler on the inside and a mandrel on the outside.

The harbor freight bender will work decent with some mods as glennpm said.

If you dont want to spend money on a bender, you could always just buy some 90 degree bends and cut them up and weld them back together how you need the. You might want to weld some lugs at the seams to keep it strong.

I usually keep some extra scrap tubing just to cut up and make rear hoop sections. What you are doing is a little more structural than just a rear hoop. But done right it should have plenty of strength.

I have done bends like those you picture with a conduit bender on 3/4 inch pipe. Don't see why it wouldn't work on 7/8. Easy if you preheat a little.

that's a better looking 90 than I made with that bender good idea thanks

weaselbeak said:

I have done bends like those you picture with a conduit bender on 3/4 inch pipe. Don't see why it wouldn't work on 7/8. Easy if you preheat a little.

Click to expand...

Hi weaselbeak,
3/4" pipe is 1.05" OD x 0.113" wall thickness.
It's more likely you were bending 3/4" OD mechanical tubing.
But if your conduit bender really was able to bend 3/4" Sch 40 pipe it will certainly cope with 7/8" mechanical tubing.

Sorry, I bent 1/2 inch pipe, just under 7/8 OD. Brain fart.

Hi weaselbeak,
for those who don't have their Machinery's Handbook in front of them, 1/2" Schedule 40 pipe is 0.840" OD x 0.109" wall thickness.

Ok you guys have giving me many Ideas. Mind is spinning. Nothing but time to do it right. I am going find me a bender, maybe go to harbor and see just what they got for the money. I knew I came to the right place. I would like to thank you all. Since I am a high end wood worker by trade, going to make me a template out of wood. When i do I will post photos. I have not worked on a bike for over 40 years and it feels great to do so now!

Thank you all so much!!!!

If you decide to use a conduit bender, get the steel one, not the cast aluminum one. And make sure they are rated for 1/2" ridged conduit (sc-40). That is the one for 3/4" EMT/1/2"ridged.

Hey Mark, Thank you for the heads up on the bender.