Hi all, I am currently still designing the machine, It will be made mainly using 20mm alu plate and 100x50 5mm box section, 20mm profiled rails sourced from chai (Thanks Jazz) and 1610 ballscrews hopefully belt driven.
Rail lengths are 1050 on X, 850 on Y and 350 on Z. Bearings are spaced 250mm apart on all axis (from outer dimension) which should give me an efective machining area of 800x600x100 excluding tool width.
Now I have used the gantry stiffness5 excel sheet and I think using the box section on the gantry I will end up with 13micron bending deflection and 30micron tool deflection. Would this be considered acceptable or the norm? If not Can you give me some Ideas to stiffen up the gantry design, I have attached a sketchup model in the zip file so feel free to modify and or tear it apart if you can help :-) Its obviously not complete yet but I dont want to spend hours on it if I am going in the wrong direction.
Will 5mm of aluminium be ok for the rails to attach to or should I glue some plate behind the box section for better securing.
One last question, I am hoping to use timing belts and pulleys, probably reduce the ratio to 75% so I should be able to get the speed for woods/ plastics but keep accuracy for aluminium, does that sound ok?
I look forward to some feedback, good or bad
Well, Quite a few views but no reply's so it cant be all bad, either that or everyone's enjoying the weather like I probably should be doing! more than likely though it is because of an incomplete design?
I have completed the basic design minus ball nut attachment and adjustable stepper motor brackets, pulleys and belts but I have some questions.
I was wondering about limit switches, Do they stop the machine dead or do I need to bring them in a bit from maximum travel and if so, how much?
Following on from that I may need to scale the machine up by about 100mm on X and Y, will the design still work or will I need to beef it up on the gantry?
I plan on using 1610 ballscrews for X and Y and 1605 for Z, is this correct.
To mount the 100x50 box section to the gantry sides I have a 40 x 40 bar cut to 90mm long in each end, would I be ok to countersink the box section and fasten with countersunk cap screws? I am assuming I can make adjustments with the cap screws on the gantry sides.
I have included an updated sketchup file, all components are models so it can be pulled apart bit by bit if you like, any feedback appreciated.
The Following User Says Thank You to CharlieRam For This Useful Post:
Gantry looks to high and the X looks to wide.
OK, I can lower the gantry by 50mm by recessing the M/C bed inside the box frame, is that enough? what do you mean by X looks too wide, the width of x rails is 850mm between gantry side plates, I cant see a way of reducing that?
Sorry I was on my mobile when I replied and it should have been a Z not an X, in relation to the width of the X the Z looks quite wide, so my thoughts where that you would be losing valuable cutting area by having the Z that size, but if your happy with the size of the cutting area you will get then it doesn't matter.
It was the same with the height of the gantry plates too really, if it was me I would consider dropping the hight down or adding another length across the X to help strengthen the whole thing up.
As I say I'm only looking at the pictures, I haven't downloaded anything.
If your mostly cutting wood then this design will be fine but if your planning to cut aluminium often then I wouldn't use it.
For wood etc then the gantry height is fine and will be more than strong enough but with aluminium you need much more stiffness so I'd change the design completely.
Lee is correct about the Y/Z axis being a little wide for the size of machine.! 200mm is what I would use on machine this size.
Leave some room for overrun when placing limits because while they do stop the Control and software instantly inertia will push the axis and obviously the faster it's traveling the more it will over run. Asking how much is like asking how longs a piece for string.!!
Yes 10mm pitch on X & Y 5mm On Z. You won't need any ratio applied to the X & Y if you use decent drives and run them with good amount of volts. You'll easily it over 10mtr/min and you won't ever cut higher than that so don't waste time and money chasing speed.
Whats the frame and bed made from.?
I haven't thought much about the base yet tbh, I was thinking of either having it mounted vertically to save space (if I decide to make X longer) or just build an aluminium 8040 table, I am assuming I will need to brace up the bed of the MC to stop twisting?
For the M/C bed I was going to use 15mm MDF and then place a 5MM aluminium sheet on top of that, drilled and tapped for t bar/ slots?
What do you think, Still not sturdy enough or will it work?
Little better but still not what I had in mind if your seriously wanting to cut aluminium. Check out the forum for machines with base frames with sides raised and rails sat on top. This design is more router biased and it will cut aluminium no problem but not with the same abilty as machine aimed directly to do this.
Also that Z axis design is bad news. Again check out threads and look at Z axis designs that put the rails on the front plate and bearings on rear. Your design is a constant length lever that won't even reach the bed surface and will give the same amount of flex whether it's at the bottom of top of it's travel. With the other design the lever length is variable dependent on material thinkness or distance from tool.
MDF for the bed isn't ideal and I certainly wouldn't waste money putting aluminium on it. MDF changes shape from day to day so if your wanting accurecy then you'll need to surface it often. Personaly I'd try to find the most stable material you can afford for the machine base, Good quality ply will work then skim surface it flat and seal or put the aluminium on that. Then use MDF as a spoil board that you don't mind cutting away or into.
Last edited by JAZZCNC; 18-07-2014 at 06:58 PM.
I will look at the Z axis, I never thought about doing it that way but now when I think about it, it makes sense thanks, I would prefer just ally for the base but its pretty damn expensive for a sheet that size, I will look into ply.
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