Finally I get the courage to join the forum and start making threads after 2 yeas of first stumbling onto it. When I first got the craze to build my own router, I got so wrapped around the idea I was going to build this incredible machine, which most of my friends don't even know what it is, I started ordering parts without any plans drawn.
So my list of components I have are,
3 sy60sth88-3008bf motors
3 pm752 drivers
20mm supported round rail for the x and y axis at 1200mm and 800mm respectively
15mm profiled rail and slides for the z axis at 550mm long
4 1605 ballscrews with nuts and mounts
a 50v minebea psu from ebay, but will eventually build my own.
All this was bought 2 years ago from Zapp and Chai, so now I have to reverse engineer my router to fit these items. I have made some detailed drawings of how I would like my machine to look, but would like some input on a few things.
Ok, as you can see I've been trawling all the build logs and tried to incorporate what I think would be best for my build.
The gantry sides and whole z axis will be made from Ecocast 20mm x 200mm wide ali plate.
The rear plate to the gantry will be 10mm thick which I hope will be sufficient.
The Z axis will have rails on the front plate and slides in the back plate.
All axis will be connected with screws using pulleys and currently at a 1:1 ratio just to get the machine moving.
The frame, which is very similar to Jonathan's, will be made from 50mm steel box section and 50mm x 100mm for the top supporting rail. I'm planing for some adjustability so will be welding the whole bottom section but will use plates and bolts for the top RHS on to which the 20mm suported x axis rails will be resting on. I won't be using any welding on this top section to avoid warping. The actual cutting bed will be height adjustable too.
A few questions I have will be described with illustrations.
The Z axis I have uses 15mm NSK profiled rails and slides. The problem here is that the total height from the bottom of the rail to the top of the slide is 16mm. The ballscrew mounts which is in between the 2 plates is 43mm thick, so I have to add 30mm of material in between the plates. I would like to know is it best to have this extra spacer added to the rails side, or the slides side. Both variations are shown in the top drawings.
This type of x axis ball nut mount looks the easiest and neatest from my side, but is it strong enough for pushing the whole gantry. It is made using 20mm plate and has 2 functions, as a nut mount and also to hole the gantry side square to the bearing plate.
I will be using 50mm ali boxing to support the y axis rails onto, but I'm unsure if the wall thickness is enough to drill, tap and hold screws from the top, and also from the back for the 10mm plate. This box section will be held onto the gantry side plates using registering blocks screwed onto the gantry sides and then a threaded rod right the way through the ali box section from gantry side to gantry side. As I've drawn above I could if its very necessary, make a strip of 10mm ali plate into a nut plate, if I can call it that. It will have holes drilled and tapped in the exact position to match the holes on the supported round rails. This way I could make the holes in the ali box section slightly larger and have some adjustability to get the rails aligned with each other.
Thanks for being patient and reading this long boring thread.
Last edited by Jonathan; 09-07-2012 at 06:15 PM. Reason: spelling mistake in the thread
Wow, at last someone has bothered to read build logs and think about it before posting
With regards to the Z-axis rail mounting - neither of those methods is ideal. If you had to pick one I'd put the rails on blocks as that would help stop the Z-axis plate bending, but they would have to be machined accurately - not just any old flat bar. However I'd consider that a last resort since it is important, particularly withnot having profile rails on Y, to get the cutter as close to the Y-axis bearings, when measured parallel to X (the 'overhang'), as you can. Since the Y-axis bearing blocks have a finite stiffness, when a force is applied to the cutter parallel to Y the tool will deflect and this deflection will be proportional to the aforementioned distance, therefore you should minimise it as it will directly increase rigidity.
As you're using standard BK/BF bearing blocks this presents a problem, since clearly they will collide with the Z-axis plate if the spacing is reduced. Options:
1) Make cutouts in both of the 20mm plates which the bearing and ballnut blocks 'sink' into, to effectively reduce their centre height.
2) Use a longer ballscrew and mount it to the Z-axis plate (like on mine), that way the bearing blocks wont be over the other plate. Still need cutout for ballnut.
3) Make lower profile bearing/ballnut mounts, then less deep cutouts are required.
Problem is all of these options are easiest with a milling machine, or require outsourcing but to me it would definitely be worth it.
The ballnut mount looks weak to me since it's so long. The easiest solution is to move the ballscrews up, but no doubt you didn't do that because the ballscrews aren't long enough to mount at the most convenient point. You could make the ballnut mount stronger, but even then there's quite a distance (measured vertically) between the X-ballnut and rail, which for the same reason as for Y/Z it's best to minimise. I would be inclined to raise the ballscrew so it is in line with the X-axis rails and add an aluminium plate to support the non driven end, preferably linking on to the far vertical support. The strength of the non-driven end bearing mount isn't critical as it's (roughly) only there to stop the screw whipping, so there's not much force on it.
I bolted my Y-axis rails to 80x80x3mm aluminium box section. The bolts are strong enough, but in my case the box section is a weak point as there is only one. You can get the necessary adjustment on the rails for them to run smoothly by drilling the holes in the rails slightly bigger to give the bolts a bit of clearance. It would be nice to use a greater wall thickness just from a strength point of view.
Thanks for the suggestions Jonathan. I've redrawn the x axis screw so it is as close to the supported rail as possible. This has bought the ball nut mount up by 60cm.
Regards the z axis. I had no idea I had to consider the height of profiled slides when I bought them of eBay. Lesson learnt, and if as you say I machine about 10mm grove out of both z axis plates, I still need 10mm. Say I grove out 10mm from the front plate, then sink the ball nut even more, up to a point where the screw shaft just clears the front plate, then I might just get away with that last ten. I'll draw this later to see if it is feasible.
I would definitely consider outsourcing to one of you guys to machine these plates as it will make a much sleeker z axis and also bring the spindle cutting point to within the x axis bearing blocks.
You should consider incorporating adjustment of one of the X-axis ballnut mounts to gain better alignment of the ballscrew. Currently you're relying on the accuracy of the frame, rail position and all sorts for the distance between the rail and the ballscrew to remain constant. In reality the tolerances on all these build up, so it's easiest to make sure at least one of the bearing mounts (clearly the non-driven end is easiest) position is adjustable in the Y-Z plane to ensure you can align it accurately. If not you risk the mechanism binding towards each end which will put a large force on the ballscrew/nut...
On my Z-axis I currently have 520mm long 20mm NSK rails, so the additional height of those helped. If you go up to 25mm plate for one of the plates on the Z-axis that might help to get the required pocket depth without sacrificing strength. Using that strategy I recently made a Z-axis using 25mm profile rails with only 2mm clearance between the plates. Also if you get the Z-axis parts machined there's not really any need to use the more expensive tooling plate - I would mill the surfaces for the rails and blocks to get them flat and in the same plane.
I was just thinking about that adjustment last night. I was going to slide the gantry to the driven end of the x axis, locate the ball screw bearing block there, then slide the gantry to the non driven end and get the position for that screw bearing block. Suppose great minds think alike lol.
Great advice about getting 25mm plate. Does that mean it would be safe to remove 15mm of material? If I don't need EcoCast then what would be suitable 6082 plate, 5083 plate or 6082 flat bar. Also how accurate does the 10mm plate that goes behind the gantry have to be? sorry for so many questions.
I basically was reading in lots of forums that 15mm profile rails would be plenty strong for all axis, but never thought 20/25mm would be better for filling spaces between z plates.
Originally I was going to make the z axis the way I'v drawn, then use a working machine to mill out what we are discussing for a version 2 machine. Thanks for offering, I will pm you about your pricing once I've re drawn it.
Like jonathan it's nice to see someone who's actually done the leg work and payed attention. . 10/10. . Big respect. .
Agree with Jonathan on every thing he's said except not using the Ecocast.! Even thou you will machine the bearing mounts etc unless you surface and make parallel both surfaces your still going to have troubles and in-accurecy. The problem comes from the cheaper plate not being uniform thickness so you can't be sure it's the same thickness (Or flat) all along it's length. This means buying much thicker than needed so it can be surfaced and still have the required thickness to be strong.
I used to do just this but since the Ecocast has been easily available in small qty then I don't bother any more and it cuts out some of the work involved and makes things that bit easier.
To be honest the 20mm plate is still fine regards strength even with the neccesary slots cut, I've made several with 19mm 6082 and slots etc and they are more than strong enough for even the most demanding jobs.! (Within reason) See pics of what you may have seen before just not striped down like these.?
(obviously more thickness will be stronger but not 20mm gets the job done.!!)
The only other point I will mention is the belt setup and the lack of protection from chips etc.!!
You probably know my machine use's this setup and I'm guilty of not covering the belts and while it's never been a problem, other than grabbing my teashirt a few times and trying to eat me, I would still advise you to cover them up before using the machine.! . . .I'm pretty sure the constant pounding from chips etc has or will shorten the belts life so worth doing before using the machine otherwise like me you'll never do it after machines put to work.!!
Anyway great work and can't wait to see it turn into reality. . .
Redrawn the z axis with new 25mm plates for the rear and front. Also included registers for the NSK rails and slides although they are only 1mm. It is a very tight fit and looks much sleeker now at only 64mm depth. I suppose If I had to then I could sink the bk/bf blocks a few mm into the rear plate, just where the blocks go. Its not easy to show but the ball nut's flange head sticks into the front plate by a few mm, which could be a good thing if the hole is machined accurately.
The spindle cutter head has now moved 30mm towards the y axis and now rests between the x axis bearing blocks. Pictures showing the new design and also how far the z extension could be dropped. Its around 250mm, not that I would need that much, but the rails are long so might as well use them. I try to put as many detailed pics up for all novices to see, as this is what I was looking for while doing my research. Hope it helps someone.
The Following User Says Thank You to Iwant1 For This Useful Post:
Ermm.!! . . . . Been looking at this thinking don't seem quite right.??? . . . I'm sure it's correct because you've obviously taken lots of time over it but I'll ask anyway just in case.!!
The bearing/rail height seems low.? from the dimensions on the drawing it appears to be about 16mm this is very low even for 15mm profiled rails and surely can't be right.? Do you have the bearings set in pockets.?
Thanks for noticing how small my profiled rails are. I mentioned earlier in the thread I didn't realise that they came in such low profile dimension. I got them for £70 from ebay for two slides and 4 rails as 15mm width and 550mm length. I've attached some pics to show their dimensions with respect to the bk/bf blocks. This is why I'm in a pickle over using 25mm plates for the z axis with 15mm machines out from each.
Do you think I should sell them on and get slightly larger rails.
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