I got a 2m long 12mm stainless steel tube to use for my shaft however it arrived bent almost in half so is hardly going to be any good, despite getting it a lot straiter, so i might as well go for a solid 12mm rod, I need it ~1.1 M long
RS sell them but in packs of 5 wich makes it quite expensive £60, although they sell them singly but in 1M lengths, at least if theres 5 they might not get so bent or bent at all hopefully, or I could chose the straightest one.
RS are good for electronics wich is my field but probably not so good for this sort of thing but im not familiar with one that is, does anyone know another supplier in the UK wich would sell me 1 x 1.5mmx12mm rod ?
Im also wondering wich is the hardest material ie will have the most torsional rigidity, stainless 303/3xx, silver steel, etc ? or if theres much difference, I can only find 1.5m in st 303 anyway.
If im spinning this at 6000rpm, will I be able to get away with a bearing at each end and 1 in the middle ? theres no load as such, only optical components.
Is there any good info on trying to straiten/balance a shaft? I have a strobe but not too sure how it can be usefull. I had thought of using 2 slightly ecentric cams to do the balancing.
Linear way shaft by Thomson, THK, IKO, etc. is straight to about .001"/ft. = and=20 ground to accurate OD.
The difference in stiffness between the materials you mentioned is quite sm= all=20 and, for all practical purposes, not dependent on hardness. The figure of m= erit=20 is "modulus of elasticity" or "Young's modulus." You'll need something exot= ic=20 like tungsten, moly, or tungsten carbide to get anything significantly stif= fer.
Linear way shaft by Thomson, THK, IKO, etc. is straight to about .001"/ft. and ground to accurate OD.
The difference in stiffness between the materials you mentioned is quite small and, for all practical purposes, not dependent on hardness. The figure of merit is "modulus of elasticity" or "Young's modulus." You'll need something exotic like tungsten, moly, or tungsten carbide to get anything significantly stiffer.
thanks, linear shaft would be realy nice, RS stock some SKF but again only in short size 0.6M I looked through the list of distrubutors on that site but none seem to have lists of stocked sizes, probably means its special order.
Id realy like to find somewhere that stocked it in the UK.
So if you can't use a decent diameter tube shaft, but must stick with a quill shaft, here's another idea for you to consider.....
Get some drill stock of the desired length. Use a conservative length/slenderness of 20:1 between supports.
For a sixty inch quill shaft, use end supports and two intermediate supports spaced at 20 inches along from each end. Make two ball race mounts. The mount will carry three ball races in a triangle around the shaft. Each provides two ball races to support the shaft from under, with a hinge and sprung closure to carry the third ball race of the trio. The major diameter of the ball races is not important, as long as they do not touch each other while spinning. That should do you nicely, and avoid the need to thread precision bearings onto the shaft.
Thanks, im an electronics/software engineer so forgive me if my attempts are painfull to watch lol, although I often do a fair bit of mechanical stuff, nothing thats needed such precision. usualy a bit of metal bending or hole drilling tapping suffices.
after a bit of emailing and ringing around ive managed to get some 12mm shaft in the post wich shld arive tomorrow.
The place I am getting it from is advertised as just a bearing stockist. The shaft manafacturer gave me their details although im not sure the shaft I am getting is from the same manafacturer.
it should be straight and exactly the right diameter and hardened to allow me to run a needle roller in the center. assuming the postman doesnt try to fold it in half again !
I cant beleive this stuff is so readily available yet there seems to be little of it advertised on the web where you can browse all the different types in stock etc. Maybe im used to electronic components where this is very much the case, maybe mechanical people arnt so keen on this aproach or dont find it necessary, or maybe electronics people are just more up to speed as its closer to their area of work. perhaps its electronics components are more varied and mechanical bits are more custom sizes. maybe theres a niche in the market here ?
Anyway, thanks for the replies.
The optical components I have are ready to accept a 12mm through shaft and have their own bearings, so will support each end of the shaft so save me making bearing housings.
With a 5mm shaft, 250mm between bearings seemed fine, so with 12mm I reckon I can get away with just a bearing at each end and one in the middle, = 500mm between bearings.
As for the center bearing, this is to go inside the motor wich sits in the middle of the shaft. The largest I can bore the center of the motor out to for the bearing is
16mm, and I have a pressed cage needle roller bearing this size this should be easy to thread onto the shaft.
however this bearing is an incredibly loose fit on a 12mm rod, and the outside diameter measures more like 16.1mm I have pushd it into a ~16mm hole in a steel plate and its a much better fit on the shaft, however im unsure if this is wise as I dont want to split the aluminium motor.
whats typical for these pressed cage needle roller bearings ? are they designed to be squashed considerably when theyr inserted into the housing to make them fit properly ? if so what sort of fit is required, or is this just a poor quality bearing thats way out of size?
Unfortunatly the machined 12mm roller bearings dont come in a small enough outer diameter to fit.
Sorry, the only needle roller bearings with which I have a passing acquaintance are those used on the big ends and mains of outboard motors, and those used in automobile prop shaft universal joints. These are close packed or slotted bronze caged. I don't think bearings are meant to be squashed. Light interference fits maybe.
Colin, You need to start thinking what's already out there. Copy machines, Automated Folder Stuffers, automotive applications, all of that stuff uses some sort of bearing in many places, often a type or roller bearing and I can imagine that you might find something that will work.
The main issue with finding stuff on the web is that the consumers of these types of industrial products just aren't computer users for the most part.
I'd contact someone like Timken and see if they can find anything in their catalog that will work. Their website is fairly complete too.
Pick a critical dimension and consider using a bushing to bring the other one (outer or inner one) to the fit for the particular bearing that is available.