Stell frame cnc 1500X1000. Adjustable table your opinion please

[ba99297]

Dean you are right. I am trying to make an all purpuse machine. In my country they said "you can not carry two watermelons under one armpit". That is what i am trying to do BUT as i am going to spend money for a machine, i am trying to achieve the best value for money project. Every day because of asking i find out things that help me avoiding mistakes. I will go on with z axis and come back. If anybody see something that should be mentioned, I will be glad to hear it. Meanwhile if you have any supplier for belts and pulleys tell me. The main problem with me ( among others ) is that I have no lathe or mill for some main machining, so I am trying to avoid that cost by sketching laser cut steel puzzles. As I see it is difficult to avoid machining. Next week I will take my plans and make a research about milling cost. Thank you so far for your help


Vagelis

[ba99297]

Here is some progress.
Ganty side plates 10mm steel. Doyou think i need a second side plate each side?
Gantry body 210mm height, made from two tubes 120X60X4 ( up down) and 1 tube 80X80X4 (middle) welded together
All gantry will be welded and then apply epoxy in order to have bottom side carriages in the same level
Z axis from 20mm aluminium and some parts from 10mm steel.
Y axis upside carriages at 400mm distance
Y axis bottom side carriages at 250mm distance
Z axis travel 200mm
Spindle plate 200mm wide

On Friday i will confirm my order to Chai for ballscrews dimensions leave 50mm for pulley attach and easy alignment
I will be glad to hear any advice or comment
Thank you for your time

[Clive S]

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

[EddyCurrent]

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

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.

[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