just read all you said and need carefully.
Some thoughts on your design that come to my mind, just what i would do., Having in mind the results you desire. I will try to resume so you dont have to look million threads for pieces of information:
- Beef up everything to 80x80x3 and the gantry to 2x 80x80x4 soldered together, or keeping your aluminum gantry design take a look at other threads to see how people do it properly with say 20mm thick plates
Beefing the structure is the cheapest thing to do on a machine. So why not do it. I have done extensive calculations and assure you that this table design is the stiffest and cheapest and lightest possible and at the same time easier to make, simple. Also doing so you avoid the necessity of diagonals. I am talking about 80x80 as ideal, to 100x100 as overbuild. I do it 100x100. You can find more info here , Tonys CNC is very good example of what you can achieve with this type of structure, of course accustomed to your needs + alu gantry
-Make the Z travel 200mm, its good compromise between stiffness and length. Take a look at how i did it here post #109 and how looks finished from 12mm steel plate a bit up at the same page. Your design will not work for that length/ or any/. The alu profile is too flimsy. Make the plate exactly as i did from 12mm steel, or 20mm aluminum at least . The plate should have ribs that dont allow it to bend in the long axis directions. In my design the ribs are the formed on the back by the steel that supports the rails and the rails themselves. Either way in front or back it must be ribbed.
The Z in question reaps fully extended through aluminum like a butter with 1/4 router bit and surfaces alu glass like finish.
-normally for multi material machine people here on forum use 1610 on all axis and 1605 on Z
-15 size linear rails is in the ball park of amateur machine. most machines that want pro results start fro 20 size linear rail, that is assumed the typical in a well made diy build. The price is almost the same.
-Hiwin from China is original. And probably the most used rail that i know of. Dont be mistaken here. Contact Fred / BST automation/ from my name and he will beat any price of linear stuff you see on ebay or aliexpress+ offers perfect machining service. You can source almost all for a build from him, including spindle and VFD. Stuff that is not listed at his store i mean.
China ball screws are acceptable, cheap and at the end do the job perfectly. Usually the quality of a build suffers from many other stuff than to concentrate on the quality of ball screws.
-on the table bed the beams should be from 200 to max 300mm separated. At 300mm you must fit sth at least 6cm thick not to vibrate. So as the steel is the cheapest thing in a build i don't see why not do it properly. Proper alu bed is very expensive. So do your self a favor and make it right.
- Now that you want 4rth axis to be 300mm OD is not a problem with 200mm axis and 2 beams separated on bed say 350mm where you can fit the axis and when not in use cover it with sheet.
-If you were inspired by Deans/Jazzcnc/ or Johnathans build to design the structure, have in mind that these machines use toolplate as table bed that makes thing very stiff.
So its not just paste and copy thing.
-Speaking about bearing spacing of bearing blocks i see as absolute minimum 260mm end to end outside measured, having in mind The long, not short Hiwin 20 carriages which each is 90mm long. That on all axis and in all directions! . Compromise can be made on the back Z plate width as Eddy said above and on the front Z plate width. i dont see though how the Z plate could be wider less than 150mm without compromising something
-that drivers you point to will Not work. you need 550-650W 70VDC non regulated power supply, and drive the motors at that Voltage 70VDC not 50VDC, so you need drivers like Leadshine AM882 which typically is the most recommended drive here. 3Nm Low Induction motors is what you need and drive them at 4.2A with the drivers at 70 VDC.
With the before mentioned you can drive all with short HTD 5M 15mm short belts and 20T pulleys 1:1, To calculate the center distances and other measures http://www.bbman.com/catalog/belt-le...alculator.html
-There are many BOB and when you search to buy happens that all of them have some trade off. Money must be spend here if yo want smooth motion. Ethernet is the way. ESS+126 PMDX board. You can buy first the board only if money is an issue. I use other board due to other reasons but it also works with ESS.
Hope that summary helps you save time fiddling and shortens the time till when chips will be flying around.
Last note is to analyse and not simply copy, cause simple stuff like simple looking structure has a lot of thought gone into it and changing little things can compromise many things, as usually the designs are quite perfected by themselves.
Last edited by Boyan Silyavski; 15-08-2014 at 10:55 PM.
I'm not a mechanical engineer, so the best way for me to learn is by burning my fingers. To do so I guess I must expose my weaknesses but have the balls to put it out there and trust folks with experience will come to the rescue - as has been the case here (thanks all). Collectively that makes of us a better, stronger community. I look forward to when I can start contributing and in so doing free up the folks with their vast knowledge to spend more (quality) time innovating and have drones like me help newbies get going .
On to the business at hand.
Not sure you saw my revisions (we posted at around the same time) but I've made some significant changes to the original. I went back to one of my 1st designs and have decided to go all steel.
If we're going to find a good shipping solution between us, my costs drop to the extent I can use Servos and an alu bed.
Thankfully there's a community of very helpful folks to nudge one in the right direction, and once you've found the proper info, you can actually do precisely what you recommend .
Thanks again for the detail, really appreciate and it'll definitely shorten my build time.
Last edited by lebies; 17-08-2014 at 08:10 AM.
The Following User Says Thank You to Boyan Silyavski For This Useful Post:
Been buying all my electronics from China for a while now, so have learned a few tricks :).
I'm thinking of pairing the AM882 with 86HS35 steppers. Good match?
Not sure I should belt-drive both X-axis ballscrews from one motor, or drive each individually.
If I go belt-driven both from 1 motor, I'll go look out around here for some examples.
If I go individual drives, what size motor should I be thinking of?
57HS09 , 57HS13 , 57SH22 , 86HS35 , 86HS38 , 86HS45 , 86HS85
But of coarse the drive can be configured for any other motor.
Are the 86HS35 Nema34 ? you should be okay with Nema23, these are the ones I use with AM882's and have loads of power/speed. http://www.cnc4you.co.uk/index.php?r...ory&path=20_27 I'm using two of them for X axis.
This thread might be worth reading; http://www.mycncuk.com/threads/6671-...-a-good-choise
Last edited by EddyCurrent; 17-08-2014 at 01:37 PM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
That in case you decide to move the gantry with 2 motors which i recommend personally. Otherwise you will need to investigate Low inductance nema 34 motor which is not easy to come by at all. In that case you can look what motor they sell at http://www.cncrouterparts.com/960-oz...tor-p-112.html. its not so easy to source such motors as one may suppose.Read more here why it matters. But may be some one here can enlighten me which China guy sell them. Its good to know.
Either I'll go 2 motors (NEMA23 3Nm my preference at the mo as well) but I'm also looking into going with belt & pulley on the y-axis, using 1 motor. Lots of advantages, just have to mess with different configs. i.e. these options (tensioners not included - yet):
Where 1 & 2 are single belt and 2 & 3 are 2 belts, 1 to each side from the center. I'll do the calcs and maybe present for comments.
I'm moving house at the mo, so will only really be online again in about a weeks time from Thursday.
Thanks so far for all your comments.
This might be worth reading, there's also a belt length calculator link in there.
http://www.mycncuk.com/threads/5146-...elt+calculatorSpelling mistakes are not intentional, I only seem to see them some time after I've posted
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