Luke11CNC Build Log ,I'm so naïve

[Jonathan]

I'd only 'force it' square using the motors if it's not much out at all. Depends on the stiffness of the frame. If it's out by more then bolt the frame down as Jazz says and if it's still not good use the formulas in mach3 to compensate as that will completely eliminate any error.

It's just occurred to be that you could purposefully have the gantry built a little out of square, force it with the motors/ballnuts to reduce or eliminate backlash. The pressure on the ballnuts from squaring the gantry would preload both X-ballnuts rather like if you have double nuts with a spring. Clearly if the cutting force is greater than that preload you will get backlash, but for light work it would work. Disadvantage is clearly extra load on the X rails and I suppose marginally more torque required, so feedrate will be negligibly less. I wonder if this is why I have practically no backlash in my X-axis...I'm not purposefully forcing the frame, but I guess it wouldn't have to be much out.

Edit: I know the T nuts did but have any of those Jigs turned up yet.?

Yes they have.

If the bearings are not all the same way it wont affect this. However the force rating of the bearings must be different in each direction as the location of the rows of balls is not symmetrical. I doubt it will make much difference, but you might as well have them aligned so it's even.

[JAZZCNC]

It's just occurred to be that you could purposefully have the gantry built a little out of square, force it with the motors/ballnuts to reduce or eliminate backlash. The pressure on the ballnuts from squaring the gantry would preload both X-ballnuts rather like if you have double nuts with a spring.

That then would just be a bodge to hide poor workman ship.!!. . . . . . . Plus it wouldn't preload the nut it would twist the nut.!. . Yes the affect would appear the same as taking up backlash but what it's actually doing is twisting Nut body onto the balls which in turn apply force against the screw. Both the screw and Ballnut are not designed to run with forces in this direction so again your forcing the screw and nut to run out of design parameters.. . . This cause's premature wear.

Much better to build right first time IMO.!!

Yes they have.

Aghh Yipee... Thanks for letting me know.!!

[Jonathan]

That then would just be a bodge to hide poor workman ship.

Or cheap ballscrews - hence why I think my measurement of the backlash might be misleading.

Plus it wouldn't preload the nut it would twist the nut.!

Maybe, maybe not. It depends what's twisting. If you assume the rails are rigid (not quite true for supported rails as they bend upon the support, but not much) then it must be the gantry in between twisting and any force not parallel to the X-axis is resisted by the X-axis linear bearings leaving only the axial force for the nut. On James' machine, clearly the weakest point on the gantry is the joint between the sides and 6" wide cross piece, so that and the cross piece will bend. The ballnut mount and gantry sides are solid so won't bend noticeably. .. etc it's obvious I don't need to tell you.

Not suggesting one should actually do this intentionally. The force ratings of the ballnuts is huge, so I think you'd get away with it. I'd be most worried about the linear bearings.

[luke11cnc]

Dear Jazz thank you for the y-axis jigs they have arrived they came on Saturday.
I would like to thank you for your time and for rushing a second set out The first set are no where to be seen
I can only now confirm this as Luke has only opened the parcel.

I did email Jonathan saying they had arrived but I was not a 100% sure Sorry for the delay

James & Luke

[luke11cnc]

I've been looking at my gantry all day and some think is not right and after about 3 hours I decided to get my set square out.


and this is what I found


The above image shows that the gantry is out of square by 1.5mm

the above image shows the joint is fitting nice and tight (this is the left side)

the above image shows the gantry is out by .5mm

am I being to picky does it really matter that much that the Gantry is not square

Well I think so

there is no stress to force the gantry out of square as all bolts have been taken out and the rails are not bolted down the only fixings is the three button bolts in the side of the gantry.

Now I have tried to force the gantry square but it is solid and will not move.

I am at a lost and getting frustrated
what is my options Please Please advise what I need to do :question::question:


James

[i2i]

if you take one side off and measure the depth of the machined groove on each edge to see if the groove is machined level to the face. It may be a good idea to machine the edge of the plate the side is clamping too, to make sure the mating faces are square and flat.

[Web Goblin]

James,
I agree with i2i on this one. It might not be the side plates but the cross axis beam. It might not be perfectly square cut or it might be slightly short. If you have bolted up one side and its a bit short it would give this result when fitting up the other side.

Ian

[luke11cnc]

thank you all Jonathan I will bring the gantry sides with me at the weekend :)

Ian and i2i the cross axis beam is not tight and only has two bolts on each side top and bottom

James

[luke11cnc]

Hello all

Well the day started of well and it was nice to see Jonathan again
I hope you liked your Hand made card and bits.

I have got a lot of bits sorted out to day BUT as always one step forward and five step's back.

My latest problem is this my gantry is 1003mm wide and with a ballscrew of 1000mm in length all look's fine on paper until you add a the belt pulley that is.

I bought the ballscrew with a standard length on the stepper end of 12mm and need 25mm.

disaster disaster two options open to me well three really

Fuck it and sell the lot

buy a new ballscrew with the correct matched machined end or make it fit.

the way I feel at the moment I could just sell the lot or just throw it away

who need this crap anyway


Sorry Just venting because I'm mad at my self and the wife has been on my case

James:cry::cry::cry:

[Swarfing]

Lengthen the screw is not that hard if you access to lathe. Dose the nut travel the whole length of the screw? I bought a shorter screw to save a few quid and did just that. So don't panic mister mannering.