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Discussion in 'CNC Mills/Routers' started by pmany, Oct 30, 2015.
Most of the way through the build, hopefully soon I will have it running
pmany published a new build:
Read more about this build...
Good job, nice that you are giving the old gantry a new lease of life.
The only issue I think you may have is in frame regidity, I made one very similar in construction but with a few extra legs and longer 45degree supports, the thing seems to be solid as a rock, but it amasing how much force is in a moving weight, i find I'm getting a wobble at beginning and end of gantry movement, so you may need to add some more steel.
I'm in process of adding more 45 degree supports so each leg has one to support every connecting bar on 8 legs and some 90x90mm box section along both sides below the base, see if that does the trick.
Recon a rule of thumb is that ideally the base needs to weight twice as much as gantry.
But other than that, great job, look forward to seeing it cutting
So the steel frame table?
I was thinking it was nice and solid 2x2 3/16 walled tubing, with 1/8 for 1x2 and 1x1 (calculated at just over 300lb). I hope it doesn't need more, I used almost all I have I might have enough to do a bit more stiffening. Once the legs are leveled on the ground I have to really work to move it, and when it moves the whole table moves with no visible flex. I will keep an eye on it though. Since this is the first machine like this I have done I am hoping I don't have any major issues. If the only issue I end up with is table stiffness I will be thrilled.
Thanks for the advice and some validation that I am not completely off base with the build.
No it's looking good, should make for a good machine. It also looks quite versatile where you could easily upgrade to square rail if you wanted to at a later date and the drive type looks as though you may have a few options available to you which is imprortant in a machine build because really it's hard to tell what issues you may find until you run it, or you may want to make it faster or more accurate.
Here is a pic of my frame, that I'm finding has a wobble.
The gantry is relatively heavy at 200 odd kg with the heavy type profiles and there some 3x3" solid bar in there aswell. so may be a little heavier than the one your using so you may be ok.
This design is a little flawed at the moment with supports only in one direction, I was hoping the 4 legs would have been enough but obviously not.
What actually helped a little was adding extra feet, I have 8 on this one. And for a quick fix I've ratchet strapped diagonals between supports to the bottom bars in y direction has reduced it a lot. Think with the 90x90 box section going under my y profiles and some y 45 degree supports it should cure it.
How much would you say your gantry weighs?
Two 20:1 planatary gearboxes with 3nm nema 23,s move it fine. 43nm each with gearing. Cuts upto 6m/min which at the moment is more than the critical speed of the X ballscrew. I am in the process of uping the pitch of the screw so I can get 9m/min and then I may want to swap the 23's for 32's but as it is it moves great @200mms/s acceleration so no issue with torque what so ever. And have had it cutting at 18mm doc at 3m/min 8mm spiral with no sign of struggle.
Nema 23's are capable of much more than you'd expect with gearing and powered correctly. 200kg gantry isn't a lot. I've seen 32's on 1 ton gantries with no gearing.
The motors run at around 70-90celcius which is what they should be if powered correctly without any overload.
Off the cuff guess I would say right around 45kg. Now I may have to take some final measurements and calculate it out...
Your machine is, very impressive.
So is that about 2.4X1.2 meters?
I would have really likes one that could do a full sheet of plywood, but just getting a machine built was a lot of work. It looks like my table is about 3/4 of yours, and your gantry\rails system is much nicer.
I was originally going to use a ball screw for the Y axis but found the gear rack to be less expensive and simpler. but like you pointed out I can still change it over at a later date.
Thanks, your machine looked like an 8x4. Oh okay it looks heavier than 47kg. Should be okay then.
Im getting only a very small amount of extra backlash on my r&p than the screw and with software correction I'm not seeing any loss in resolution in y as with my screw in X, so really the r&p is as effective and you don't need to worry about whip and sag so personally I'd have done the same.
Mines not quite, its 2.7 X 1.5 with a cutting area of 2.3 x 1.3m. It was very much a compromise, I wanted it to be able to mill Ali so I made the gantry deeper than you would often find on woodworking machines to improve rigidity. Unfortunately the longest square rail I could get was 2.7 otherwise I'd have gone for 3m but I can lay an entire sheet on the bed so it's no real drama, if I need to cut parts from an entire sheet I simply cut the parts within the 2.3m area then spin the sheet and the origin in my cam and do the remaining bits.
I will eventually get myself I milling machine and it will be that I dedicate this one to woods and plastic in which case simply cutting the gantry plates less deep, moving the back carriage in and cutting the 3x3" solid bar that spaces and runs the depth of the plates so as to give me a 2.4x1.3 cutting area.