FEATHERBED RAKE ANGLE

Hi all
I seem to have stirred up a hornet's nest here - unfortunately some correspondents are getting overly hyped up over what should be an interesting biker/biker discussion, not an excuse for slagging each other.

Again might I state my simple query: I wanted to know what is the correct angle between the headstock and the bottom frame rails of my slimline featherbed. SIMPLE QUERY. Unfortunately I received various answers from various sources, most claiming to be based on factory specs (but I could never locate these mysterious 'factory specs', nor did anyone direct me to where they could be found).

Just a couple of points:
I have scoured my posts and can find no first reference of mine to 1/2 degree - this was referred to by Rohan in his post of May 26. Apologies to Rohan re my inference of his contribution on Ken Sprayson - a typo error on my side.

With regard to Unity Equipe not touching slimlines, they most certainly advertise them for sale, and have done so for a long time!

With regard to 'no featherbed was 27 degrees', I'm afraid this statement does not agree with the info I have received from Maidstone Motoliner (via the kind offices of Nick from Classic Bike) which states that the headstock/bottom frame rail angle should be 62-64 degrees (ie 26-28 degrees from the vertical when the bottom rails are horizontal). This angle is 24 degrees in the diagram posted on the NOC website.

With regard to the bikes being made by different companies in the early 1950's and the Slimline era - certainly true, but they were made by the same company (AMC) from 1953 (when the featherbed first became available for the production models for the home market) until its collapse in 1966 (after 7 years of supplying wideline models and 6 years of slimline)- subsequently, the remaining few featherbed models were trickled out by Norton Villiers until 1970. In any case, throughout its lifespan of 20 years the featherbed frames were made by the one manufacturer - Reynolds. This information is documented by the NOC.

The statement by Carbonfibre that the headstock/bottom frame tube angle is immaterial does not make any sense at all. I would hope that we all know what a rake angle is and so will not bother to explain. However, when building a frame the builder needs to be able to reference the headstock to some other part of the frame - otherwise he could just throw it in at any old angle and sort out the rake with front and rear suspensions, front/rear wheel sizes etc - not very practical!

Similarily a frame realigner needs to have some way of referencing the angle of the headstock to some other part of the frame - he cannot just angle it to a skyhook! On a featherbed the bottom frame rails provide a handy reference plane as they can be easily set in a jig.

Finally, as I have said before, Ken Sprayson could set us all straight (ha ha) on this as he was the MAIN MAN in the 50's and still is - I am still trying to get in contact with him, just to be sure, to be sure. When it comes to a featherbed, Ken is the man!

Keep her lit.
Matt
 
The 1/2 a degree comes from your words. Slimlines were said to be made to 24 degrees - you mentioned that Ken Sprayson reckoned they were 24 and a half degrees.
That is a half degree difference, is it not ?
And as I pointed out, that is probably within the manufacturing tolerance of frames anyway, 1/2 a degree isn't much.

If you line up a slimline, a wideline, an early 750 and an 850, you can just about see the angle differences. If anyone claims that slimlines are the same angle as Commandos, see the chopper Atlas here.....
http://i.ebayimg.com/00/$%28KGrHqMOKicE ... -!~~_3.JPG

P.S. Somewhere, I tried a set of disk Commando forks and yokes on a wideline. The proximity of the wheel to the frame tubes suggested this was not a wise setup, before it ever turned a wheel.
Commando did funny angles with the fork tubes for the steering stem with slightly more rake...
 
P.S. Try ordering a slimline frame from Unity.

To quote their website.
"We have tried to incorporate the most popular features from the many different types ie; international, ES2, Dominator. Some were bolt up, some had tail Loops) We have a large collection of original frames, no 2 are exactly alike, so we have arrived at a Universal type."
In T45, so the material is different too. Hopefully better, though.

Pics of their frames show this - it is exactly unlike anything sold by Norton.
If you want genuine replica featherbeds, try Ken McIntosh in NZ.

Some time back, someone here did a Hinckley Thruxton engine in an Atlas slimline, this was the neatest cafe racer. On seeing the picture, Unity (Jackie) stated at the time they were doing wideline frames, and would never touch a slimline. Even though the head could come off in the frame in the slimline, but not in their version.
Unity still make a nice cafe racer though, good that someone is feeding this market too.
 
Rohan,
Thank you for your continued interest in this topic.

However, you continue to misread my posts; nowhere have I "mentioned that Ken Sprayson reckoned that they were 24.5 degrees".
Please recheck and inform me of where I have said this, I CANNOT FIND IT, I DID NOT SAY IT - THIS IS QUITE CLEAR, IS IT NOT? - if you can find it I will abandon this English language lark and return to conversing in my native Gaeilge as obviously I have been unable to master the idiosyncrasies of English, and indeed am unable even to decipher my own writings.

With regard to your remarks on the Commando, I know nothing of them other than that the differences between the 'early' and 'late' yokes are well known and documented with all widely available brand new from several well known and knowledgeable sources.
Matt
 
Does it matter that much whether someone really said something or someone else just thinks they might have?
 
Mattyboy, repeatedly, told me I said it, so obviously it does...

Sidecar yokes were available, for sidecars obviously, wonder what angle they were ?
This is an interesting point - your yokes are not stamped with S/CAR on them somewhere are they ? This would only affect the fork tubes angle though, not the steering head.
(How did you measure your steering head angle ?).
 
P.S. Commando steering angles and yokes quirks can't be too well known - when I pointed out on the NOC-L list that late Commando fork tubes pointed "backwards", this was rubbished by a number of seasoned C riders - until I showed some yoke pics, and they went and actually looked at their own forks... !!
 
mattyboy said:
Hi all
I seem to have stirred up a hornet's nest here - unfortunately some correspondents are getting overly hyped up over what should be an interesting biker/biker discussion, not an excuse for slagging each other.

Again might I state my simple query: I wanted to know what is the correct angle between the headstock and the bottom frame rails of my slimline featherbed. SIMPLE QUERY. Unfortunately I received various answers from various sources, most claiming to be based on factory specs (but I could never locate these mysterious 'factory specs', nor did anyone direct me to where they could be found).

Just a couple of points:
I have scoured my posts and can find no first reference of mine to 1/2 degree - this was referred to by Rohan in his post of May 26. Apologies to Rohan re my inference of his contribution on Ken Sprayson - a typo error on my side.

With regard to Unity Equipe not touching slimlines, they most certainly advertise them for sale, and have done so for a long time!

With regard to 'no featherbed was 27 degrees', I'm afraid this statement does not agree with the info I have received from Maidstone Motoliner (via the kind offices of Nick from Classic Bike) which states that the headstock/bottom frame rail angle should be 62-64 degrees (ie 26-28 degrees from the vertical when the bottom rails are horizontal). This angle is 24 degrees in the diagram posted on the NOC website.

With regard to the bikes being made by different companies in the early 1950's and the Slimline era - certainly true, but they were made by the same company (AMC) from 1953 (when the featherbed first became available for the production models for the home market) until its collapse in 1966 (after 7 years of supplying wideline models and 6 years of slimline)- subsequently, the remaining few featherbed models were trickled out by Norton Villiers until 1970. In any case, throughout its lifespan of 20 years the featherbed frames were made by the one manufacturer - Reynolds. This information is documented by the NOC.

The statement by Carbonfibre that the headstock/bottom frame tube angle is immaterial does not make any sense at all. I would hope that we all know what a rake angle is and so will not bother to explain. However, when building a frame the builder needs to be able to reference the headstock to some other part of the frame - otherwise he could just throw it in at any old angle and sort out the rake with front and rear suspensions, front/rear wheel sizes etc - not very practical!

Similarily a frame realigner needs to have some way of referencing the angle of the headstock to some other part of the frame - he cannot just angle it to a skyhook! On a featherbed the bottom frame rails provide a handy reference plane as they can be easily set in a jig.

Finally, as I have said before, Ken Sprayson could set us all straight (ha ha) on this as he was the MAIN MAN in the 50's and still is - I am still trying to get in contact with him, just to be sure, to be sure. When it comes to a featherbed, Ken is the man!

Keep her lit.
Matt
Click to expand...


Since I gather that you are building a special the frame doesnt have to be correct to the original design right? You could just alter it to an angle that you want, you could even get carried away and make it adjustable with eccentric collars in the head tube. Another thing to consider is how the attitude of your special willl compare to that of an original featherbed, fork length, shock length, spring rates, sag and wheel size, engine position and mass etc.
 
WITH REGARD TO FEATHERBED SIDECAR YOKES (courtesey of the great gentleman John Hudson over 20 years ago):
The top yoke is stamped s/car to the right of the top column nut. On the bottom yoke - (the crown and stem) - the column is not parallel with the fork stanchions but pulls them in at the top to push the front wheel forward and so reduce the trail. Additionally the crown is straight across instead of being a shallow inverted 'U', and instead of the underside being completely flat with a hole approximately 5/8" in diameter for the boss on the lock stop plate to centre in, it has a much larger diameter hollow boss over which a lock stop plate with a large diameter hole - from memory 1&1/4" - fits, with a friction disc above and below and then a threaded cap into which the steering damper rod screws clamp the the two friction discs together with the lock stop plate between them and this cap is made to turn with the forks by a pear shaped extension and a set screw which secures it to the underside of the crown. Additionally, the lamp brackets/fork top covers are 1/4" or maybe 5/16" shorter than the solo parts.

My yokes are certainly not sidecar type, the top is a John Tickle and the bottom is standard featherbed resulting in the stanchions being parallel to the column.

I measured my headstock/bottom frame tube angle by driving a perfectly fitting and perfectly straight steel rod through the headstock bearings, while having the bottom frame tubes lying horizontal in angle sections which extended to intersect the rod. The intersection angle was thus able to be measured, and was subsequently checked by photographing in the side-on plane, importing into AutoCad, superimposing linear vectors onto the image and dimensioning the angle.

With regard to different Commando yokes, RGM in Cumbria are but one supplier who can provide all off the shelf and list all in detail in their extensive catalogue. They have a great reputation for the quality of their stuff and their customer service. Similarily, Andover Norton and Norvil list the different Commando yokes along with the appropriate nuts, washers, bearings etc.
Matt
 
The guy that was doing replica Atlas frames reports Atlas frames used 24 degrees.

Does anyone doing Commando yokes advise the forktube angles etc, or just sell the bits.?
I've not seen a good rundown of the geometry. Not that I've needed it, jist curious.

Likewise the sidecar yokes, of which I have a set. No sidecar though, so not chased it either.
 
I've done more than my fair share of AutoCAD superimposition and measurement, and that can very easily be off by more than 2 degrees from a photo.

...for whatever THAT'S worth...
 
Taking a front downtube as having a straight section of 500mm, a line superimposed at 2 degrees offline would result in an error of 17.5 mm after a run of 500mm. The OD of the tube is almost 32mm, so for a superimposed line to be 2 degrees off it would require the line to be drawn from the bottom edge of the tube to over 1/2 way across the tube at a distance of 500mm. I don't think that I could draw that badly even without glasses and a skinful of Guinness on board. With use of a high resolution camera and a high resolution VDU, along with appropriate correction factor for perspective if required where a wide angle view is involved, high accuracy is not a problem.

Rohan, I have seen figures for Command steering. When I locate them I will let you know.
Matt
 
I'm not really interested in a bunch of debate, but for what it's worth:

Unmolested 66 atlas frame measures a hair over 24 degrees.
Unmolested 68 atlas frame measures at about 24.5 degrees.

I've also got a 56 dommie, but it's had a pretty rough life and I wouldnt want to take it as fact, but it comes out to just over 25.
 
"no two alike"

I wonder what the factory's QC allowable margin of error was?
 
My Wideline when sitting on bottom rails measures 24degrees. I know this because the stake ( Donkey's Knob) which ran up through the headstock when I true any twists is welded to the "former" plate at 24 degrees.
Its not concours.... it just goes
 
Hi All,
I have eventually found the answer which is unquestionable in its veracity.
After a lot of trying I was in the end able to contact Ken Sprayson - Ken oversaw the production of all the featherbed frames in their long production run at Reynold tubes. A real gentleman - he replied to my query promptly in a beautifully handwritten letter. Ken in his own words 'positively confirms' that the headstock angle for all featherbed frames should be 64 degrees with respect to the bottom frame rails; in the manufacture of the frames this was never altered. The rake is of course dependant on other factors such as suspension set-ups. Anyone doubting Ken's knowledge of the frame should check out his letter in the 2011 August Roadholder magazine where he enlightens us all regarding the engineering solutions used to counteract headstock problems which showed up in pre production testing of the mild steel featherbeds.

This query has been now truly put to bed! I can now take my frame to my MOTOLINER man and provide him with the correct info to work with.

Matt
 
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