Frame Jig

[Slider29]

Out of curiosity and maybe need later on,... what is involved in making a jig to replicate a frame
eg. 1975 Godden (side port). I have access to an original.
regards  Mark

[Iain Cameron]

Come in GMC . Slider29 after looking at Geoff's jigs I would say quite a bit of work is needed .

[SON]

bill Rawlinson in Newcastle

[mick25]

Yes GMC would be good for tips
 You can get adjustable jigs to make any frame , with adjustable length decks , head stock heights and deg angles to suit what you want.
or make your own custom job and copy off your frame.
all needs to be spot on off cause and you need a bit of welding and metal fab back ground would help.
do a google search on frame jigs theres lots of info from pros and back yarders having a go.

[Slider29]

 yeah Son, I heard that Bill has Godden jigs. Any contact details? thanks.

[SON]

I have Bills number at work
I will PM them tomorrow

[Slider29]

Thanks Mick25,
I have access to everything required,....welding, tube rollers, steel fabrication etc. Thought it might be fun to have a go. A slider frame is  pretty basic. Antig make complete forks so all that is left is the main diamond, sub frame and swing arm. The old Godden frames are pretty hard to find.

[Mick D]

Hi Mark, I have no intent to manufacture repo frames, more money in just going to work, But I am building a universal frame jig.
I have measured many frames very few are straight, that is very few have a swinging arm pivot axis that is perfectly square to the head stem axis. I am using 250mm universal "I" beam(RHS) with 10mm thick web section as a rotating rigid bed member.
The swinging arm pivot point is rigidly mounted. The steering head mount is not only robust, but fully adjustable to stress the frame back toward its intended alignment, while heat is used to entice it to yeild. Naturally the rear upper shock mountings have a similar adjustable positioning arrangement.

As suggested, my intent is to straighten and produce quality repairs to some of my many frames.
As with all fabrication repairs and straightening it will provide correctly directed straightening forces and bracing alignment whilst cooling and stress relieving.

It is a position lockable rotisserie to achieve and provide the optimum position for ease of welding and penertration.

[GMC]

Frame building jigs and frame straightening jigs are built differently.

Frame straightening jigs I have seen are basically a rectangular cube frame made from heavy duty RHS that the bike frame can sit inside of, the headstock of the frame is held securely and the RHS cube frame that surrounds the whole frame is used with a porta power and other chocks to manipulate the frame to where you want.

Bob Martin was pretty switched on with frame straightening and he told me many years back now ( he has since passed away) that he would straighten brand new frames, mostly for superbike racers as production tolerances weren’t up to scratch for serious racing.

I imagine this may have changed with alloy frames as most frame parts are cast and CNC machined so there would be less distortion during fabrication


The more complex the frame the more complex the frame building jig.

Frame building jigs need to be solid enough to not move or twist, they need to support all the important points like engine mounts and swingarm mounts as well as hold all tabs and frame tubes in place.

All my frame jigs have removable sections to enable the frame to be removed once assembled.
Dealing with distortion is another issue again

From the GMC secret files…
Took me over a week to set this one up and this one went together easy as I’m more experienced at it now.

[Lozza]

More than one amature frame builder has not got the frame out of the jig after construction 

Next is getting the head stock to swigarm pivot absolutely at 90deg to each other, not 89.9 or 90.1 but 90.00deg.

Next hurdle is decent material, either DOM/CDS/T45/Renolds or CrMo tubing is not cheap and usualy only can be purchased in 4 or 6m lengths.

As for construction I don't have much experience but fitting a tube inside 2 other tubes isn't as easy as it looks. Especialy if each end is at a different angle. Dry fitting seems to take 20 goes to minimise the gaps.

In the end I found it a very time consuming activity.

[Slider29]

Thanks for the input fellas. I reckon I might have a go at building a frame later on.
Just to see if I can (with the help of a mate).
regards  Mark