Thread: Build and Intro
Been a bit of a dweller and thought I better introduce myself and show my build, asking lots of questions in the process.
I'm from the land down under, Australia, it seems pretty much all of you are in the UK!
The frame is made out of 65x65x4 mm box section steel. I think I may have gone a bit over board in this department, I'm sure you'll be able to tell me if its too much or too little. Originally the rails being used (all 20mm fully supported round rail) were going to be 1600mm for x 1000mm for y and 300mm for z. When I went to buy them there were no 1600mm in stock so I got the 1800mm for the price of 1600mm. This also forced me to get 1600mm ball screw instead of the planned 1400mm ball screw. The thing is I had already built the frame so now the x rails overhangs one end by 200mm. Instead of just cutting the rail I thought it would be good to leave it and modify the frame to accommodate it by adding a triangular section under each rail. This will allow me to do cuts that otherwise wouldn't be able to be done.
To level the table I will be using the self leveling resin method. I've already drilled and tapped all the holes for the x rail so these holes will obviously have to the bolts in them when I do the resin. What do I do to stop the resin from sticking to the bolts?
Cover them in a little oil?
I was thinking of using fiberglass resin. Anyone had any success with this? Other options?
Now the gantry.
I really cannot find anyone that can supply any suitable aluminium section for the gantry. This means that I have to use steel. For a length of 1.2m do you think 200x100x3 mm will be sufficient? I'm a bit worried about the weight of it. That section just mentioned will weigh around 12kg. The two sections that will hold it above the x rail come in around 13kg. Thats around 25 kg with nothing else added or accounted for. The x axis is moved by a 425 oz-in nema 23 motor. Will this handle it? It will be run with 1610 ballscrew, one on each side with belts. 5mm pitch 15mm wide htd belts and pulley will be used. Thinking a ratio of 1, can be swayed either way though to change this ratio.
Both the other axis will be powered by, I think 312 oz-in nema 23 motors.
Are all these motors alright to be run at about 60-70 volt? Heres the drivers I brought
3 Axis CNC Kit Stepper Motor Driver Controller 2M982 Interface Breakout Board | eBay
I hope these will be okay??
I think I'll be asking lots of questions about the electronics part when it comes to that so be prepared!
And the spindle brought
1 5KW Water Cooled Milling and Grinding Spindle Motor with Inverter Drive VFD R3 | eBay
Again any specific things I should know about this spindle?
Also through reading the threads I've read its better to have the supported axis rail for the z axis on the bit that moves up and down. Why is this?
I think thats enough for now.
Thanks and will eagerly await the replies.
To protect the bolts from resin I just covered them in grease and they came out easily. For the resin you want something with the lowest viscosity you can find and a long setting time, to maximize the chance it has to self level. I'm not sure if the viscosity of polyester resin will be low enough, probably not? The resin I used is west system 105 with 209 hardener.
Don't concern yourself too much with the weight of the gantry. What's more important, to have a strong machine or a fast machine? Your answer is almost certainly the former, so make it as strong as you can and then worry about possibly needing a bigger motor. Since you've already got the motor you might as well try it, but 3Nm is a bit on the small side. If you got another of the 425 oz-in motors and drivers, then connected one to each X-axis screw you would have enough power to move (at least) a 50kg gantry at a decent feedrate and acceleration.
Shame you got the 1.5kW spindle not the 2.2kW one. The 2.2kW spindles come with ER20 collets, so instead of holding up to 10mm tools they can hold 1/2" tools. That's useful if you want to use cheap router cutters.
Generally putting the rails on the part of Z that moves up and down reduces the overhang, i.e. the distance between the tool tip and the linear bearings.
Have you done a drawing of the gantry? It's a bit late now but it would have been easier to make a strong machine if you'd gone for an adjustable height bed and had the Z-axis working below the level of the X-axis rails, like in my build logs. Still, if you're not planning on cutting metals then you'll get away with it.
Thanks for the fast reply jonothon, good man. On the train at the moment so wont do full reply. Are the photos showing up out of interest. Almost certainly wont be using machine for metals 99.5 percent o the time.
So the build has been coming along slow as uni is getting in the way.
I used the west system resin recommended and it worked really well. However it could have been a lot better if i had of sealed the edges better as quite a bit dripped out so there were some low spots.
The x axis is nearly complete, I'm just waiting on the belt and pulleys to arrive. I ordered 20 tooth pulleys and a 2525mm long 5mm pitch 15mm wide htd timing belt. Belts will also be used for the other two axis.
I had to use steel for the gantry as no one would supply the aluminium I needed. I could only get aluminium if I brought a 6m length.
I'm having a bit of trouble with working out how to arrange the bearings for the z and y axis. I know I asked in my first post about mounting the supported rail so it moves with the spindle but I want to know how important this is?
I ask because it will save a lot of mucking around if I can mount it the other way with the bearing blocks on the spindle.
21-10-2013 #5I could only get aluminium if I brought a 6m length.
I think another reason for putting the Z rails on the moving plate is to add stiffness to the plate, you could argue that the rails should not be used to add strength but undoubtedly they will. There are plenty of machines with the rails mounted both ways and likely it will work both ways, it's just that one way is slightly better than the other.
Machine is looking good by the way, I can see the frame is well put together but I don't see any triangulation such as diagonals. Will you be fitting adjustable feet ? or maybe your floor is flatter than mine. As Jonathan says the 2.2kw ER20 spindle would have been so much better and I suggest you should go this route to have the 1/2" capability.
I found the round rails to be a bit bulky for the Z axis but they do allow more space for the ball screw.
I could have done that but a bit meh with the fuss involved.
I think I will mount it with bearings moving with spindle. It just makes everything a lot easier. I'll take into account the lost rigidity of spindle mount without the rails. 20mm thick aluminium seems to be the standard isn't it? I think it should suffice. And yes having some hywin type rails would be nice but the ballscrew is the limiting factor at the moment as I can't machine into the aluminium so their profile could be lowered. Hmm maybe a project after this is complete is to make a new z axis with hywin rail.
The table is bolted to the ground in 8 spot(one each leg) so I'm guessing this might mean I don't need triangulation?? Will wait and see. The epoxy leveling was done after. This means that I can never move the machine(as it would have twisted when I bolted it down), at least without redoing the epoxy each time.
I'm going with 20mm aluminium plate. It sound like a good idea to fasten the machine down but I think you could still have adjustable feet too just in case
I'm not an expert on cnc (yet ) but from your pictures, my past engineering life and what I've learned from this forum, I'm thinking the square tube bracket down to the x axis ball screw is not strong enough. It would be better if there was a triangular fillet each side to prevent flexing, I can imagine it vibrating causing tiny oscillations.
Last edited by EddyCurrent; 21-10-2013 at 02:25 PM.
Regards the rails on front then mostly depends on how much extension you have on the front plate when cutting and also what your cutting. If mostly extended and cutting harder materials, hard woods,aluminium etc then it will make enough of difference to matter. Low extension and softer materials it will hardly make difference.
Thanks for the replies
How tight should the belt be? As in should I be able to turn the pulley on one side a little bit(maybe 8th of a turn) while holding the pulley on the other side still? It runs between the two sides and has a center distance of about 1100mm.
Also with the pulleys the length of the bore is about 29mm and it has two set screws. The shaft for the pulley on the end of the ball screw is only 15mm long. Should I be concerned that the shaft isn't long enough? Is tightening down the set screws onto the round shaft fine or should I grind down two flat areas on the shaft for the set screw to tighten onto?
Re the belt tension - you need to minimise backlash, 1/8 of a turn is way too much. Use one of the online belt calculators to see what the centre distance should be - it will depend on pulley size. If you can't get the exact centre distance you will need an idler pulley or other tensioner - e.g. a bearing on a stud pressing against the back of the belt.
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