FEATHERBED RAKE ANGLE

Interesting. If anyone should know, it would be Ken Sprayson. Thanks for contacting him and posting his response. As you suggested, I've just checked the down tubes on my slimline frame with a straight edge, and it does have a bend in it. Although it appeared straight when I looked at it yesterday, the straight edge shows up a gentle bend in the right direction to reduce the head angle. I can only conclude that it may well have started out at 26 degrees, and later been bent back to 24 by something like a head-on collision. Guess I'll have to check the rest of it now, and plan on straightening it before use.

Ken

J. M. Leadbeater said:

It should be remembered that the frame was originally designed as a race frame and NOT a road frame and that Reynold simply produced them to Norton supplied drawings and that they Reynold had a policy of 'the customer is always right so thats what we will produce' along wwith a policy of not offering advice to customers unless it was specifically requested by the customer when it would be given based upon their decades of experience......

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Actually, if you look at road going featherbeds and manx frames, it will be noted that the steering head in the road bikes is boxed in with quite extensive gussetting - which the race frames didn't get.

And if you study the blueprint thats being bandied about as being for the roadgoing slimline, the 2 front downtubes both have an inserted tube inside to reinforce them.

Bill Cakebreads' book on his AMC years have an account of (some ?) featherbed frames being produced with the wrong steering head angle.
The blueprints didn't match what was actually being produced ??
Bit of a vague account, the truth is out there, somewhere...

The gusset was introduced in an effort to keep the head stock at 26 degrees but all it did was to ensure that the down tubes simply flexed / bent where the gusset plate ended!! That is why on later frames another piece of steel tube was drawn into the main tube in a final effort to keep the head stock at 26 degrees. the inner tube had to be drawn in as it had to be a tight fit because if it was not it did nothing to strengthen the main tube.
It really should be remembered that Reynold Tubes merely manufactured these frames to Norton drawings and had nothing to do with their design. Had they of done so then I suspect the frames would of been nothing like the ones we ended up with. Reynold were experts in the field of tubular frame design and construction and were more than happy to offer advice to customers IF ASKED FOR IT. I repeat IF ASKED FOR IT. Their attitude was that the customer was always right.....and I suspect along with ' and when the customer makes a balls up its their fault and we make more profit putting it right'. I heard that Reynold made more profit sorting out each Italian made Commando frames than they did when making them correctly to drawing themselves in the first place!! Some clever soul, probably an accountant, decided it was cheaper to have the frames made in Italy...... It wiould of been had they been correctly made but as one NVT gentleman once said to me of the Italian frame maker....'....they made and still make very good frames but not to the price NVT wanted to pay'.
It was only someone with a brain asking for Reynold Tubes to suggest a cure for the total cock up that was the origional Commando frame design that resulted in the Commando frames being sorted out to stop the main spine failing big time.(See the photo on page 147 of Volume 2 of the book 'The Racing Motorcycle' for a picture.....) That is yet another amusing tale.......as is the one describing the testing of 3 versions of Commando frames on a cobbles test track..... The origional frame design failed after 26 laps, the AMC expert suggested thicker spine version failed after about 120 laps and the thin wall tube but with the extra bit of tube beneath it to triangulate things suggested by Reynold was a bugger and refused to fil even when evenyually sent scrambling on the tank test course!! Guess why Commandos ended up with this Reynold version!!
Yesterday afternoon I made a phone call to Birmuingham... Aster a natter with Mrs Sprayson I was handed over to Mr Sprayson and asked him to refresh my memory on how our Dommy frames were manufactured....... It goes something like as follows..
The main tubes were bent around 4 formers to make complete loops.
These were inserted onto a frame jig and the cross tubes etc welded in.
The jig complete with tubes was taken to a BIG drill. which had its base set up to position the jig in the correct position and at exactly 26 degrees.
The 4 tubes in the head stock area were trepanned out to accept the headstock.
The headstock was welded in and the bearing seats given a final machining to correct size... (welding distorted the head stock).
When I made my Domirace frame jig the trepanning was done by the electric motor / reduction gearbox etc which was part oif the jig .....kepr me amused for months working out how to do it AND it works perfectly....I I always knew that long lump of 10 inch steel U channel I fell over hidden in long grass on a radar site would come in handy one day!!
When tales of different headstock angles first appeared many decades ago Mr Sprayson had a chat with the production side at Reynold who told him that the base of the BIG drill was never changed and stayed at 26 degrees throughout its existance and that the drill was ONLY employed for trepanning the head stocks..I.E. it was a there for doing one job ONLY so the base was never touched and stayed at 26 derees throughout its lifre.
Thus I would suggest any frame found with a head stock of anything but 26 degrees is bent and you only have to run your bike into a 4 inch kerb and you will bugger the headstock ESPECIALLY on Manx frames!! Talked to an even older than me friend last night who has always run Nortons including Manx models on the road and he stated that the ONLY frames he had ever had that were straight were on new bikes bought direct from the factory and that every second hand frame he had ever used to build up a bike with had to be straightened first.....He actually has his own featherbed straightening arrangement...to get the head stock to vertical he has two brick walls he shoves the frame between, shoves a BIG long tube down the nead stock and twists it....to set the 26 derees he does something similar! Bent featherbed frames were so common Reynold Tubes ran their own featherbed straightening service...bring it in and we will sort it ...dont know if it was a while you wait service mind you as I never bothered to ask!!!
So if you frame is not at 26 degrees as it probably wont be get a straight edge on the back of the down tubes along every mm of length you can and see where the bend is. Bet its at the end of the gusset plate.....
Of course my frame maker friend who now has my Domirace jig sitting in a shed ready for future use for customers who want Domirace frames often has people asking him to modify head stock angles for competition use..... On 27 degree frames he pulls them back to 24 degrees to make then go round corners faster BUT you had better fit a steering damper for straight line stability. I am told BSA employed 27 degrees to aid straight
line stability........

Re AMC making frames with the wrong headstock angle..... Ever visit AMC?? Ye gods it was a dump just like our local Hoffman bearing factory... Nothing coming out of AMC would of suprised me and I had a friend serving his apprenticeship there so we had weekly reports on the latest cock ups that occured.....mind you he would take a crank in in the morning and bring it home that evening with a new FREE big end fitted....... Both would of made perfect Victorian industrial museums!! Tis s no wonder neither still exist, rather like most of British industry ...mind you we still have the CBI or Chanber of British Incompetence as I refer to it so everything is OK!!
No spell or grammer checks done..I hear the call for dinner.

When you tighten the turnbuckle which joins the rear of the steering head to the manx motor, how much does the rake change ? When you change the rake from 26 degrees to 24 degrees on a manx frame to get it to go around corners faster, there is no easy way to alter the offset on the yokes without producing yokes which look totally non-standard. The handling of the bike is based on wheel size, rake and trail, wheelbase and rear suspension setting. A production manx under power is very stable and confidence inspiring and probably self-steers slightly. Some of the replica frames made in Australia steer like Suzuki two strokes, you don't take a smooth line into corners, you steam up to them and tip in. The difference in rake between non-self steering and neutral steering on some bikes must be in the region of half a degree, because they will actually steer on the throttle as the rear end squats if the bike is cranked over in a corner.

Changing the steering geometry on your bike is the easy way to get a crash, if you cannot recognise the symptoms your changes deliver. Once when my bike stood up and turned the wrong way as I braked towards a corner, I didn't know what was happening and it threw me off-balance. I knew I was gone, so tried to drive the bike to the grass verge on the outside of the corner for a more gentle crash. The bike came back under control - arse beats class.
Tony Foale has done a lot of work in this area.