Jig to Hold Head in Lathe
- Thread starter Marcus Bowden
- Start date
Ina bearing 20 x 33.
Thats better as the 2 narrow ball ones.....
Thats better as the 2 narrow ball ones.....
No jig needed for the dozens of these I've done, just a sunnen hone.........jobs done in no time........Just be careful the needle rollers can have play in them once assembled........any for and aft play in the steering head area will produce a noticeable "Clunk" from the front end on the road.
I have organised over 100 of these to go with the JE steering stems. Note, I do not do the machinimg. It is normal to find that the holes at the rear of the lower link are worn oversize, some to the extent that the 32 mm O.D. ball races fall through. These have to be bored and fitted with a steel bush before the bearings. I have seen very few where the hole was not worn and nearly all lower links no longer have the eyes in line. For those contemplating doing their own please note that it is important to check whether the link is still true and relatively unworn before starting any machining. It needs a good jig and/or some skill to ensure that the final job has the eyes exactly in line and parallel with the bores of the two front bushes, FF6.
Nice job, Vincent. But now you got the trouble to keep water out of the bearings - with little space left for seals. Not my business with my Bramptons, but I would never mess around with bearings in this place. Don´t see the benefit of zero friction with balls or needles there when you want a factor higher compression or extension damping from the hydraulics. So my idea was IGUS line-reamed bushes there, no lube and very low friction. For damping set the hydraulics to reasonable forces and scrap the old spring struts with their own lubrication dependend springs inside. The IGUS should do a lot more mileage on stainless excentrics than the contemporary Vincent owner will see in 20 years. No, I don´t see how that tad of friction in these bushes might come in the way of damping by the hydraulics. They are not an electronic contraption to mess with hydraulics, just smooth and minimal resistance from low friction, only a fraction compared to damping within the damper.
My guess, lots of girdraulic components today come with twisted links and the new bushes get reamed somehow for some fit , far from perfect. So the ride will be somewhat stiffer than could be had with all perfect geometry within the girder forks. Not an easy job on any girder with all spindles and bushes finished with piloted reamers definitely. So don´t blame just the old bushes for stiff ride when reasons may come from older defects , unidentified by present owners.
As to jigs for boring crankwheels, not a worthwhile thing for one engine - and unsafe in use for perfect positions. My advice, have the wheels set up on a simple mill with DRO and a low tech boring head. No exact aligning of bores is critical, just roughly set up in one axis. Then get zeroed center of mainshaft bore by checking with clock in mill spindle . Then do same in crankpin bore and note position on DRO. You get funny numbers certainly as you did not carefully align in first place. No drama, get out the trigonomy , enter the half stroke as hypotenuse and calculate sides of triangle. So then you can shift final calculated positions for cleaning up the old crank pin bore and have exact hypotenuse and half stroke.
This is to get an exact half stroke datum in the old bore for next step :
When you like to have a minimal taper seat in wheels to go with tapered crank pin you will do this on a lathe , no way with a boring head on mill. So bolt the wheel on a base plate on your lathe and center it perfectly with clock on new datum, plus add some counterweights on base plate so the lathe won´t wobble much when finishing the new bore at low speed certainly.
You want a real good finish in the bore , otherwise the microscopic surface mountains in the taper or parallel press fit will get ironed flat in use and the strong fit gets weak. Look at other modern pressed up cranks, crank pin bores will most likely be circular ground , not just milled or turned .
The Vincent crankwebs appear to be medium tensile steel, so high press fits unsuitable then. So when a mod is looked at you could do a real strong job and go for a taper joint with 1 or 2 degrees set on lathe PLUS have the shouldered crankpin sit on the faces of wheels - best joint you can do at all. I did this on a 600 cc Horex single so yes, you can !
The minimal taper will get you good strength from twisting loads - like Morse tools - plus the shoulders will help fight bending loads in the wide crankshaft. To do the machining safely you have a dummy crankpin made with standard thread on so you can do a test and torque down the dummy pin and check the amount of axial gap to shoulder when the crank pin is drawn into the 1-2 degree taper. So you then have a new tapered crankpin made and the lathe crankwheel finish boring can be done to have exact shoulder gap like you tested earlier. For finishing the crankpin bore I got me a hf spindle from China plus VFC for finally have a perfect finish and easy precision grinding of taper fits in combination with shoulders bolted up with nuts as standard.
My photo below shows this bore grinding on base plate. I had a big alu spacer under the crank as mainshaft and wheel is one piece. The grinding wheel in hf spindle is not a grinding stone as I fond them very critical for sudden vibration and wrecking the bore in a second. I turn up an alu wheel in suitable diameter and wrap a strip of abrasive around it with a little help from instant glue . Sounds incredible I know but I swear it works great in through bores with some patience. Once the abrasive gets too blunt it will fly away, no drama, glue a fresh strip on and proceed as before - minimal stress for fitting in fractions of a thou .
Yes, you will spend some Pounds on tooling, hf spindle, DRO and so on, peanuts in Vincent world I say. But alteratives to home equipment for getting anything done in reasonable time will become less and less likely. So best way is upgrading your workshop as much as you can, it pays.
Vic
My guess, lots of girdraulic components today come with twisted links and the new bushes get reamed somehow for some fit , far from perfect. So the ride will be somewhat stiffer than could be had with all perfect geometry within the girder forks. Not an easy job on any girder with all spindles and bushes finished with piloted reamers definitely. So don´t blame just the old bushes for stiff ride when reasons may come from older defects , unidentified by present owners.
As to jigs for boring crankwheels, not a worthwhile thing for one engine - and unsafe in use for perfect positions. My advice, have the wheels set up on a simple mill with DRO and a low tech boring head. No exact aligning of bores is critical, just roughly set up in one axis. Then get zeroed center of mainshaft bore by checking with clock in mill spindle . Then do same in crankpin bore and note position on DRO. You get funny numbers certainly as you did not carefully align in first place. No drama, get out the trigonomy , enter the half stroke as hypotenuse and calculate sides of triangle. So then you can shift final calculated positions for cleaning up the old crank pin bore and have exact hypotenuse and half stroke.
This is to get an exact half stroke datum in the old bore for next step :
When you like to have a minimal taper seat in wheels to go with tapered crank pin you will do this on a lathe , no way with a boring head on mill. So bolt the wheel on a base plate on your lathe and center it perfectly with clock on new datum, plus add some counterweights on base plate so the lathe won´t wobble much when finishing the new bore at low speed certainly.
You want a real good finish in the bore , otherwise the microscopic surface mountains in the taper or parallel press fit will get ironed flat in use and the strong fit gets weak. Look at other modern pressed up cranks, crank pin bores will most likely be circular ground , not just milled or turned .
The Vincent crankwebs appear to be medium tensile steel, so high press fits unsuitable then. So when a mod is looked at you could do a real strong job and go for a taper joint with 1 or 2 degrees set on lathe PLUS have the shouldered crankpin sit on the faces of wheels - best joint you can do at all. I did this on a 600 cc Horex single so yes, you can !
The minimal taper will get you good strength from twisting loads - like Morse tools - plus the shoulders will help fight bending loads in the wide crankshaft. To do the machining safely you have a dummy crankpin made with standard thread on so you can do a test and torque down the dummy pin and check the amount of axial gap to shoulder when the crank pin is drawn into the 1-2 degree taper. So you then have a new tapered crankpin made and the lathe crankwheel finish boring can be done to have exact shoulder gap like you tested earlier. For finishing the crankpin bore I got me a hf spindle from China plus VFC for finally have a perfect finish and easy precision grinding of taper fits in combination with shoulders bolted up with nuts as standard.
My photo below shows this bore grinding on base plate. I had a big alu spacer under the crank as mainshaft and wheel is one piece. The grinding wheel in hf spindle is not a grinding stone as I fond them very critical for sudden vibration and wrecking the bore in a second. I turn up an alu wheel in suitable diameter and wrap a strip of abrasive around it with a little help from instant glue . Sounds incredible I know but I swear it works great in through bores with some patience. Once the abrasive gets too blunt it will fly away, no drama, glue a fresh strip on and proceed as before - minimal stress for fitting in fractions of a thou .
Yes, you will spend some Pounds on tooling, hf spindle, DRO and so on, peanuts in Vincent world I say. But alteratives to home equipment for getting anything done in reasonable time will become less and less likely. So best way is upgrading your workshop as much as you can, it pays.
Vic
Vic, I admire your tool room and talent in using it. Most of us are just lucky to have a mill and lathe. My approach works well other than the mirror finish. Once bolted to the mill the 1" thick aluminum plate is bored and reamed. The main shaft for both flywheels is pinched in the plate then the pin bore is located 60mm in to match the stroke or what ever your stroke is. This motor is 120mm stroke. While still in position a lap is used to get a finer finish. This setup is also used to check or refinish the crank pin abutment so it's perpendicular to the new crank pin.
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Is the eccentric FF7 hard enough as a needle bearing surface?
On all the ones I have been involved with the FF7 is not used. What one is doing is to alter the centre of rotation for the rear of the lower link. A stainless steel concentric is used on all the JE stems that I provide. What one is trying to do is to alter the path that the front wheel follows when going over a bump. This is achieved by moving the centre of rotation both forwards and downward. It should be noted that the first time we used Greg's modification, with bearings rather than Oilite bushes we, Chris Launders and I, thought that the AVO damper had failed, so dramatic was the reduction if frction.
Again, friction can have its very different causes, poorly aligned bushes can be one of these. And what´s so bad about some slight friction when you get a suitable damper then ? You want a LOT more friction - well, hydraulic damping it is from the damper for rough road use and I don´t think friction in modern "plastic" bushes is a factor then.
Litnman,
your thinking is allright when having a bit of honing the bored crankpin hole later in the mill for better surface finish and size. This with parallel pin as standard. What oversize do you aim for in standard wheels resp. in your specials - different kind of steel I guess ?
When having a taper pin plus shoulder it is not an option certainly, cannot hone a taper. My toolroom is tiny in second floor with my favourite lathe, the mill is in the unheated garage. For upgrading these machines costs will be below € 1000.- for DRO and all today, nothing compared to what you´d be prepared to pay for spares or jobs by companies you were lucky to find at all.
Vic
Litnman,
your thinking is allright when having a bit of honing the bored crankpin hole later in the mill for better surface finish and size. This with parallel pin as standard. What oversize do you aim for in standard wheels resp. in your specials - different kind of steel I guess ?
When having a taper pin plus shoulder it is not an option certainly, cannot hone a taper. My toolroom is tiny in second floor with my favourite lathe, the mill is in the unheated garage. For upgrading these machines costs will be below € 1000.- for DRO and all today, nothing compared to what you´d be prepared to pay for spares or jobs by companies you were lucky to find at all.
Vic
30mm more stroke! Is it a Vin? I wouldn’t have thought that there was room.