Luke11CNC Build Log ,I'm so naïve

[JAZZCNC]

I'm not trying to flog it at all. I was just pointing out then that it is wrong to say there is any significant twisting force on the screw, and therefore you're only increasing the axial force on the ball-screw which is the same as what would happen if you did it properly with double nuts and a spring. If it wasn't for the large force it places on the rails I see no reason not to do it. It is obvious that there are far better ways to attain low backlash. I mentioned it originally more to point out how it could lead to a false reading of backlash.

Well It wouldn't be acceptable to me or a practice I'd employ on any machine with my name to it.!! . . . . So again we'll have to agree to disagree.

Oh you might want to checkout how proper double nuts are connected and preloaded.? Dont think you'll find meny springs around.?

[Jonathan]

Well It wouldn't be acceptable to me ... on any machine with my name to it.!!

Same

Oh you might want to checkout how proper double nuts are connected and preloaded.? Dont think you'll find meny springs around.?

I know, but proper double nuts aren't as good as two nuts and springs / belville washers are they.
When I referred to 'double nuts and a spring' earlier I was thinking of doing something like this as it's a simple way of implementing it:

http://www.mycncuk.com/forums/showth...ull=1#post8924

Especially with only C7 grade screws where the pitch error limits how far you can go with double nuts.

[JAZZCNC]

I know, but proper double nuts aren't as good as two nuts and springs / belville washers are they.
When I referred to 'double nuts and a spring' earlier I was thinking of doing something like this as it's a simple way of implementing it:

Ok as my final comment on this.!! . . Yes and no. Yes Belville washers will apply far more preload but at the potential cost of shortend life.! There is such a thing as too much preload.
So then for that very reason NO it doesn't make them better.!! . . . .They will only be better for shortened period of time, obviously how long depends on Belville force, but they will wear sooner with the ultimate result of a wornout knackerd screw.
If good quality screws with high preload doublenuts are used they will give zero backlash with trouble free service for years, if installed correctly and maintained properly.
Yes they come at an high cost but theres a reason for that, precision costs.! . . . . If it was just a simple case of sandwhich a few Belville washers between 2 std nuts without any consiqences or performance costs then thats what they would do dont you think.?

Anyway all of this is Ballcocks for 99.9% of DIY level machines and certainly cheap C7 chinese screws.

James I appologise for filling your thread with unrelated post's so know I will say no more unless related to your specific build, which this originally kind of did.!

[Jonathan]

So then for that very reason NO it doesn't make them better.!! . . . .They will only be better for shortened period of time, obviously how long depends on Belville force, but they will wear sooner with the ultimate result of a wornout knackerd screw.

I think the spring method will be better for longer as wear with the double nut will lead to more backlash, whereas wear with the sprung nuts will not have much effect. It will reduce the preload a bit, but you can adjust it so it guarantees that backlash is eliminated. Which is pretty pointless on a router anyway...but I know which method I'll be using when I convert my lathe/mill.
Either way for hobby machines they are used so little (relative to in industry) than wear on the ballscrews/nuts is negligible. If you've used it for long enough to wear out the ballscrews then you've probably made enough money to replace them.

James: That not being quite square is one reason that I suggested you used triangular plates from the X-bearing mount to gantry side. They will stop the deflection.

I cut the slots in the gantry sides on my router as they wouldn't fit on the mill. The bad had been surfaced recently, so they shouldn't be far off ... if you want me to skim the bearing mount plates to get them square that's not problem. I meant to do it anyway but forgot.
Bear in mind SBR/TBR type bearings will tolerate some rotational misalignment, so will it make a difference when the machine is running? I don't think so, but I'd still add reinforcement triangles to make sure.

[JAZZCNC]

I think the spring method will be better for longer as wear with the double nut will lead to more backlash, whereas wear with the sprung nuts will not have much effect. It will reduce the preload a bit, but you can adjust it so it guarantees that backlash is eliminated. Which is pretty pointless on a router anyway...but I know which method I'll be using when I convert my lathe/mill.
Either way for hobby machines they are used so little (relative to in industry) than wear on the ballscrews/nuts is negligible. If you've used it for long enough to wear out the ballscrews then you've probably made enough money to replace them.

Ok jonathan you seem to know something all the top Ballscrew manufacturers in the world don't so get on with it and good luck.!!

James first I would double check the square is accurate.? Those type of wood working squares are not the best for accurecy.! Ideally you want a good engineers square, longer the better.

The gantry is not neccesorally out of square, check the angle between the cross brace and gantry sides.! . . . Are they 90deg.?
Like as been suggested the cross brace could be short or the rebates in the gantry sides could have been cut fractionly deeper than intended creating the same affect.
If the difference is only small then you could easily place a shim/s in the rebate effectively widening the gantry back to original width and/or use them to bring back into square if rebate is uneven depth or wedged shape.?

Because your using round rail you can accomodate this slight angle difference were the bearing plate meets the gantry side. (Easily fixed with with triangle braces like Jonathan suggests)
Thou it's actually not a big problem if the gantry sides are not exactly 90deg to the cross brace because your using round rail. (If was using profiled rails then yes it would be a big deal.)
Yes ideally you would like absolute square and true but So long as the error is not so great that it affects the screws then you'll be ok

Far far more important is the gantry runs square to the X axis.

I say get your self a good accurate square and some shim steel, It's not un-common to have to use shims to bring things into line or back to square so dont consider it a bodge.!
Far better to hold something square with shims than force it square.!!!

[Jonathan]

Ok jonathan you seem to know something all the top Ballscrew manufacturers in the world don't so get on with it and good luck.!!

All the top manufacturers are aimed at industry where the expectancies (life, accuracy etc) are significantly greater. So if we slightly reduce the life by using double nuts or springs with the same preload it's still going to last a very long time. Most DIY builds don't lubricate the ballnut which clearly is reducing the life expectancy similarly to what we're discussing, however they still run for years... I did consider lubricating mine properly, but when you're rotating the nuts it's easier said than done. Even if you could connect the tube for the oil the oil just flys out.
My comments apply to the C7 screws almost all of us buy where the spring helps compensate for the lead error, not your C1 ballscrew!

James: You can check how accurate the square is by placing 4 equal diameter cylinders in it arranged in a square and measure the diagonals (i.e. placing the caliper across the tangents). If they are equal you know it's good. That's fine in theory... the problem is finding 4 accurate cylinders, bigger the better-I don't advise using your router's rails!

[blackburn mark]

If you've used it for long enough to wear out the ballscrews then you've probably made enough money to replace them.

thats the way iv been looking at it :naughty:

Ok jonathan you seem to know something all the top Ballscrew manufacturers in the world don't so get on with it and good luck.!!

thats a tad aggressive jazz .... in this sport there is an element of "art" and "on the cheep" im struggling to knock jonathans logic till i know better..... out of interest has anyone managed to wear out a ball nut in our DIY circle ?
and did they make enough to replace them lol

[JAZZCNC]

thats a tad aggressive jazz

No "Your talking bo@~#cks Jonathan" is Agreesive but I didn't say that did I.:whistling:

Yes I've worn out a ballscrew, it took 3 yrs and yes it payed for it's self meny times.