Motorcycle Frame Tubes

[martin seymour]

Hello All. Above is a picture stolen from the web. It's of the famous Norton Featherbed motorcycle frame. As you can see the main frame is constructed with two loops of steel tubing running from and back to the head stock being braced by the engine and gearbox assembly.
In my case being a road frame the main frame is made from 1-1/4" od x 14 guage (2mm) mild steel tube.
I would like to remove the piece of curved tube between the two red lines on the picture to replicate the earlier version of this frame that had an 8" radius bend instead of the later 6" rad. - sleeving inside bfore brazing or welding. I have been advised by a frame builder that doing this would compromise the rigidity of the design.
I don't understand this - Does anybody have any thoughts about this?

 

[frank horton]

ur not building a high stress street racer....?
no worries on frame stregnth, the weakest point is around the weld joint.......
the v/old days frames were brazed..
modern tech would use mig or tig....
here's the ultimate tigged braze....

lookat my avatar......I have to build frame and forks for that.....abso no used frames .....

where poss, all my will joints will be sleeved....

 

[Shox Dr]

I cant see a problem with a Sleeve and rosette weld. The frame will most likely be ERW tube so you will need to get rid of the weld spew inside, to be able to fit a sleeve

 

[addjunkie]

I cant see a problem with a Sleeve and rosette weld. The frame will most likely be ERW tube so you will need to get rid of the weld spew inside, to be able to fit a sleeve

I cant see an issue with a sleeved joint either. However depending on the age of the pictured frame, not sure it will be ERW. The guys down in wales who was building replicas was using chrome molly T45 tubing If my memory serves me correctly.

What you will find when you cut it to replace the bends itll move all over the shop, so be prepared for it.

If you google Norley frame jig, theres video of the replicas in the frame jig, will give you an idea!

 

[8ob]

I am no motorcycle frameist but i think it should be braced/jigged up before you cut it. Maybe extend the verticle modified tube down past the rear mount a bit to get more structural weld on that section of tube.

Bob

 

[JEZGUZ]

The early frames had a bolt on rear subframe, I think your easiest option is to buy one from somewhere like Stafford or one of the other auto jumbles and flog yours to recoup the costs. You'll have to remake the subframe on your frame if you chop that section out.

 

[brightspark]

norton frames were made from reynolds think it was 725 or 531 seamless tube not just mild steel. cutting it open will let the stresses out not the best of things to do

 

[Seadog]

531

 

[redlig]

norton frames were made from reynolds think it was 725 or 531 seamless tube not just mild steel. cutting it open will let the stresses out not the best of things to do

And is tricky to weld /braze or whatever. I'm not so sure that 531 was used in the road frames or only in the comp ones. Someone will know .

 

[Morrisman]

Friend of mine has a reproduction Featherbed frame with a Sportster motor in it, building a cafe racer, but he is no engineer and that's about as far as he has got, it's been sat in his shed for a decade or more now.

 

[martin seymour]

Thanks for the replies. Yes I'd have to build a jig before cutting it. The Racers were made from 16 gauge Reynolds Chrome Moly tubing but alas this is a roadsters frame and would of been made from Mild steel CDS.
Would it be better to braze the joints if the braze could be presuaded to flow further into the joint or tig/mig?

 

[Shox Dr]

I cant see an issue with a sleeved joint either. However depending on the age of the pictured frame, not sure it will be ERW. The guys down in wales who was building replicas was using chrome molly T45 tubing If my memory serves me correctly.

What you will find when you cut it to replace the bends itll move all over the shop, so be prepared for it.

If you google Norley frame jig, theres video of the replicas in the frame jig, will give you an idea!

The OP says its 14g, so unlikley to be anything fancy. And yes it will spring open.

 

[CompoSimmonite]

I'm not sure what you are trying to achieve. Is the different radius needed for engine clearance or is it just for looks ? Personally I'd sell your frame and just buy one of the earlier versions you require.

 

[martin seymour]

Mmmm - CompoSimmonite - I was hoping for technical advise

 

[brightspark]

you got good technical advice no need to heed if your comfortable doing it your way

 

[addjunkie]

Thanks for the replies. Yes I'd have to build a jig before cutting it. The Racers were made from 16 gauge Reynolds Chrome Moly tubing but alas this is a roadsters frame and would of been made from Mild steel CDS.
Would it be better to braze the joints if the braze could be presuaded to flow further into the joint or tig/mig?

If its just mild steel tubing, and I were doing it, Id stick it on my frame jig, to make sure the head stock and rear axle position / swingarm pivot dont go out of of alignment. Id then brace the frame with extra metal to prevent the cut bits moving. Once cut Id drill through the remaining frame say 8mm, then make both new tubes and the slide in sleeves. Id also drill the new bits too, and assemble. Then plug weld with a welder of choice through the holes. Id then weld the but joint, making sure to pick up the sleeve too. Plug welds add a bit of strength, but if you were not on a jig would be easily drilled out if its all gone a skew. Before you fully weld up. Then re attach the seat hoop

 

[tom2207]

Friend of mine has a reproduction Featherbed frame with a Sportster motor in it, building a cafe racer, but he is no engineer and that's about as far as he has got, it's been sat in his shed for a decade or more now.

no point in rushing it ,,

 

[Shox Dr]

There's a lot of strength through a rosette weld and butt using a sleeve with a thin wall tube.

45* butt is better than a straight 90*
Do not drill through the sleeve.
Hole size should be a 1/4 of the tube diameter, and a 1/4 of the dia from the tube end. 2 per side 180* and part. 90 to each tube

 

[Nomad]

I saw a write up about featherbed frames many years ago that said the final bend on the frame "sprung" everything into position.
Expect it to *unsprung* when you make your first cut.

Given how desirable the frames are now it makes sense to buy what you want and sell your uncut original.
Photos or a build thread would be a good idea

 

[martin seymour]

There's a lot of strength through a rosette weld and butt using a sleeve with a thin wall tube.

45* butt is better than a straight 90*
Do not drill through the sleeve.
Hole size should be a 1/4 of the tube diameter, and a 1/4 of the dia from the tube end. 2 per side 180* and part. 90 to each tube

This sounds good - but could you clarify "2 per side 180* and part. 90 to each tube" please

I saw a write up about featherbed frames many years ago that said the final bend on the frame "sprung" everything into position.
Expect it to *unsprung* when you make your first cut.

Given how desirable the frames are now it makes sense to buy what you want and sell your uncut original.
Photos or a build thread would be a good idea

Now that's a thought - would that tension in the 'spring' add to the frames rigidity?