new build opinions required

[Boyan Silyavski]

Silyavski If you are thinking of Linuxcnc and need to slave motor on one axis there is a problem with homing that has not been ironed out yet. See here LinuxCNC Support Forum :: Topic: Homing and limits with X axis 2 joints (1/2) and here LinuxCNC Support Forum :: Topic: Configurate Slave Axis (1/4) This might be being fixed in the next release. ..Clive

Thanks for the info. Though here is what i think of it in my case, may be concerning this build also:
-if the machine is rigid like mine and like this will be , may be it shouldn't be a problem. With Hiwin 20 HA bearing spacement at the gantry sides of 40cm/ or even 30/ i don't see how it would go out of true, its not a flimsy machine we are talking about here.
-i would use servos, they will simply stop due to error

again, a few very important bits of info between you lot there.


2 rails per x axis side, one above, one below, 2 barings per rail, seems to make the most sense on an equal loading/force approach. Maybe its not a bad idea to have the barings as the week point, Because they are cheeper to replace in time and money, compared to unbending a machine gantry. If, from the design stage, you consider the barings as consumables ( not to short a life time though ). it free's up some design options.

I still don't like that design of yours, but that shouldn't discourage you :-)

R&P suits a heavy gantry, and i can see why most heavy machines use it, but, when your building your 80k to 100k + to sell to a customer, the customers not going to acsept thaty every n100 hours of running, they will have to replace the barings, and every n1000 hours , the ballscrews, so you design a machine thats heavy enough to absorb the forces, to give your barings and ballscrews some help. but the extra weight requires bigger motor or servoes, and causes other problems, or pushes you design in certan directions.

I don't know if i am understanding you wrong. But:
RP is far more wear prone than ball screw. Ball screw is far more better and smooth. for 6m long table, yes RP, but for anything under 3m-ballscrew.

wereas, if you specificaly design your machine for the barings to be the week point, you can make you Y gantry a box, that contains a Z Axis, thats a box iteslf with rails on both insides of the Y gantry. The hole Y ganty, clamped by rails and barings on the top and bottom of the X axis, with the ballscrew in the gap between them (between the edge of the Table frame/X axis and the Y ganrty box ).

IMHO the weakest points in order of a DIY machine FYI:
1. Router bit - deflection
2. Z overhang-plate twist
3. Gantry twist and bend ,
4. Gantry sides
5. bearings/assuming you use square
6.Spindle power
7. Balscrew support bearings, spindle bearings
8...etc

My main reason for designing like this, apart from equal forces in all directions, is machine down time if a mistake is made, This is through experiance of owning/running a Gocarting track 97-2001. Go carts have lots of expencive barings in them, and after 2 years of large parts bills, we redesigned and refitted the frames, to eas of on the barings, What a mistake, we spent a lot less on barings that season but down time per cart frame due to bending was horrendus, each frame had to be stripped and bolted in the jig for 2 days, heated and coolded, then brazzed, then rebuilt, That job went from once after the end of each season, to frames queing up to be placed in the jig.
My point being, make a mistake and bend your machine, your down time is a lot more (maybe days ), and you dont know what the cost of repair might be, whereas, if you pop your barings, its costly, but you know how long it will take and how much it will cost before your machine is running.

You can not bend with steppers a properly constructed machine. They will simply stall. Remember this. Nor you can wear Hiwin bearings if properly mounted. When you have them in your hands you will see why. They will be probably that last element in a machine to fail.

Back to the BOBs

I have another questions in mind concerning the BOBs. Please some one more knowledgeable clear it for me:

-With steppers: If Mach 3 outputs as max 100kHz pulse/ even less normally/, then a normal reliable board that supports 100khz should be ok, yes?

-With servos: If Mach 3 outputs as max 100kHz pulse/ even less normally/, then why should i care to buy a board like the CSMIO or other? I know, apart from the reliability and connections, i mean. Every modern servo drive can upscale by gearing the frequency and generate the proper signal , so why waste money on expensive cards that will do exactly the same thing in fact? I start to believe that the driver generating the pulses will be quite better and reliable..
It seems that mach3 is the limiting factor, not the board?