Straightness of steel/alumunium box section

[Ross77]

They should do, they are rated for 862N/1372N which is well above the cutting forces. I'm not sure about the torque ratings of the bearings though which is probably more of an issue.

Ok i will try to explain, but im not the best. Maybe some else can re-phrase my ramblings......

Basicly you have a force at the cutter that is then transmited over a distance to the bearings (force x distance = N/mm) if nothing is able to resis this force then it will rotate about the centre point. In this case it will be in the middle of the 4 bearings, so yuo will have 50mm from the centre line to the bearings.

So say you have 10N cutting force over the 350mm (for aguments sake) thats 3500 N/mm, now as all forces have to equal and opposite (one of Newtons laws.....) the bearings will have to resist the 3500N/mm but only over 50mm so the bearing wil see 3500/50=70N

So you see that the actual force on the bearings isnt just the cutting force and in this case is 7x the cutting force, although divide that by 4 and each bearing will onlys see 17.5 N from the cuting force

It's 160mm wide and the centre distance of the rails is 100mm. I don't really understand which torque you're referring to that could make a difference to the Z rails?

Its the centre line of the rails that counts, as far as the lever arm is concerned. theres also the fact that a long thin beam will more suseptable to vibration........( but that a whole over can of worms):naughty:

The danger is that this calc only deals with cuting force and on the face of it makes the bearings look overkill. In reality there all sorts of other forces that need to be allowed for. but rather than spend the rest of you life trying to calculate them just make the machine as ridgid as can and then cross your fingers :whistling:

[Jonathan]

Ahh thanks for the description. I was thinking in the wrong plane...now it makes sense!

I'll put the rails right on the edge of the plate since that gains about 10mm.

rather than spend the rest of you life trying to calculate them just make the machine as ridgid as can and then cross your fingers

Yes, I'll make it as it is now. I'm currently waiting on my Mum/Dad to give me permission to buy the bearings. Then I hope to find somewhere better to buy the aluminium plate!

I'm intending to have this router finished before I start University, so 21-09-10.