Stell frame cnc 1500X1000. Adjustable table your opinion please

[ba99297]

Have you thought how you will access the mounting bolts on the Z rail blocks (4.jpg) it looks like the Y rails blocks will restrict them. On another point it seems like you are use angle iron for the rail blocks (Y) are you sure that they will be at true right angles and that the inside edge is flat and parallel to the outside edge. ..Clive

Yes this will be an issue according to these plans but the above plans are only for giving a general idea about the machine. Specific issues ( as the one that you have mentioned ) i think will be solved with small conversions. As for the iron angles the most possible scenario is to have them perfectly milled or use aluminium angles that are more accurate.

Aluminium angle is a lot more accurate than steel so maybe you could use a thicker section aluminium angle instead.
Do you need the full Z travel ? if not I would move the Z Hiwin blocks further apart.
Also now is the time to work out where your cable drag chain (energy chain) will sit, you'll need three lengths of the stuff and will need to know the lengths, bend radius, internal dimensions.

Looks like it's coming together nicely.

According the plans z axis rails are 400mm the ballscrew (full length ) 501mm carriages distance (outer side 200mm) . That will give z axis a full travel of 200mm. May be ( if that will make the construction better) i will put the carriages at 250mm distance and reduce the full travel to 150mm.

Question 1
The above conversion worth the effort ?


Question 2
Also I would like to say that I choose to put the Y axis ballscrew at the front of the gantry in order to have the ballscrew as close as possible to Z axis and at the same time having the ballscrew exposed to the off cuts of the spindle.
Is that correct ?

Question 3
Do you think I will need a second side plate at both edges?


Thanks for your time

[EddyCurrent]

Question 1
The above conversion worth the effort ?

Maybe you could put some figures in the stiffness calculator and find out, http://www.mycncuk.com/forums/linear...html#post15791

Question 2
Also I would like to say that I choose to put the Y axis ballscrew at the front of the gantry in order to have the ballscrew as close as possible to Z axis and at the same time having the ballscrew exposed to the off cuts of the spindle.
Is that correct ?

My machine has the ball screw at the back and so far I have noticed no problems.
Some people put a plate over the front with a slot for the ball nut bracket, you could fit these to the slot, Toolstation > Ironmongery > Draught Excluders > Heavy Duty Brush Strip
or keep it like it is and use two of these to keep swarf out Machine Bellows - Arc Euro Trade

Question 3
Do you think I will need a second side plate at both edges?

I would hope it is strong enough as you have it now with one plate but again maybe you could try putting it into the stiffness calculator.

[Jonathan]

Roughly in order of priority...(i.e. in order of how much I expect these changes will impact the overall stiffness of the machine:

1. The thin plates the linear bearings are mounted on are definitely weak points.
2. Keep the Y-ballscrew where it is - it's well positioned. Moving the ballscrew to prevent exposure to swarf is totally the wrong priority - just guard it if necessary.
3. The spacing of the bearings on the Z-axis is a bit low - bear in mind the deflection of the linear guide system is proportional to that bearing spacing squared, so every little helps.
4. Try to compact the Z-axis to reduce overhang - by making cutouts in the plates you should be able to avoid putting the rails on spacer strips.
5. The Z-ballscrew could be made shorter if you want, but it doesn't really matter.

You only need the adjustment slots for mounting the X-axis linear bearings to the gantry at one side - on the other side you could use normal holes and mill a reference edge for the bearings to rest against. That will help slightly with getting things square. It's also a good tactic for the other axes - particularly Z in your design.

[ba99297]

Roughly in order of priority...(i.e. in order of how much I expect these changes will impact the overall stiffness of the machine:

1. The thin plates the linear bearings are mounted on are definitely weak points.

Jonathan when you say "The thin plates the linear bearings are mounted on " you mean the carriages of X axis of Y axis or both X and Y axis?
The "thin plates" of X axis supposed to be 10mm iron. What thickness is suitable ?

The spacing of the bearings on the Z-axis is a bit low - bear in mind the deflection of the linear guide system is proportional to that bearing spacing squared, so every little helps.

I suppose you mean to increase the distance between the 2 lower and the two upper carriages and that will reduce the Z axis travel

Should i need a second side plate?


Thanks
Vagelis

[ba99297]

After Deans sujestion i put the y axis rails at the front

The clearance from the table to the spindle collet is 115mm

Thanks for your time

[Jonathan]

We've established that the weight of the gantry is not something to be concerned about, so no need for those cutouts between the Y-axis bearings. It'll be stronger if you leave it as a rectangular plate.