Should I make a magnetic head assembly that would support different attachments?
a duel extruder attachment
a diode laser attachment
My thought is to make the duel extruder attachment mount to a pcb that everything connects to. This will allow for simple wiring. The pcb will have 8mm diameter magnets mounted to the four corners. The pcb will be able to be used for either assembly. The print head slide will have 8mm diameter steel bolts at the four corners for the magnets to attach to. This will keep everything aligned, also allows for micro adjustment to the head alignment.
Let me know what you think. Would this be something you would be interested in? Or is there no point?
I tried a magnetic attachment myself on my coreXY and I needed much more than a 10 pound pull magnet, but my design was vastly different. It depends on how the different extruder setups will rest on the carriage. From the looks of it yours is cradled which is a good idea. Also a couple of dowel pins for alignment and XY plane stabilizing wouldn’t hurt.
@Kyle1 you are correct the pcb sits on top just under the extruder motors. So I think I can get away with small magnets. I could easily add the pin you mentioned. Good idea. Thanks for your input. I followed your build. You make a nice machine. I would like to upgrade to the slides you are using but they are not very cheap. Also I went with the single belt duel motor drive for XY. Shooting for 434mm cubed duel print volume.
You should be ok with running a direct drive setup for the XY motion motors. But having such a large build volume requires very long XY motion belts which will need a ton of tension to get as much of the slack out as possible. This will also add stress to the bearings in the steppers, so you might look into adding a bearing plate on the other end of the motor pulley so that it is not stressing the motor bearings as much. Bigger idlers will help ease the load on the XY motors. Also running the motors at 24V would help tremendously if you aren’t planning on doing so already.
O yea I almost forgot! I have a hell of a time tensioning my belts by hand and keeping the X axis straight while trying to get even tension on the belts. I would suggest that you build some kind of tightening tool for each belt that allows you to fine tune the tension while also being able to check that the X axis is straight. Something that you can place on the gantry and then remove once the belts are tight and X axis is parallel.
@Kyle1 man that is awesome information. I currently don’t have this completed, was planing on running 24v. The pulley and iddlers I purchased already, they are not big, 20 teeth size gt2 6mm belt. Didn’t think there would be much of a problem getting it tight. But i have never had a setup this big either. So what are your toughts about those tension springs made for gt2 belts? If I mount two of them to the head and have the belt tighten by having those pulling on them constantly. One pulls from the left lead end. The other pulling from the other end. Or should I look at making a loop at either end and stretch a retraction spring between them and figure out some way to mount that to the head?
As for linear rails. It really pays off to spend the money on quality linear rails. Trust me. I have done multiple 60+ hour prints and my Hiwins are doing great. I know you are planning on doing some pretty epic prints with such a large printer and it is nice being able to rely on the printer to produce great prints. I have ordered some linear rails for other projects from this ebay store: http://stores.ebay.com/industrialpartsshop/
I have been very happy with the used rails I have received from them. Also check periodically on eBay for new in box overstock linear rails and carriages. Aliexpress is a good place to get genuine Hiwins as well for cheaper than eBay.
Those tension springs for gt2 belts will be no where near strong enough to take out the slack. Everything changes when you up the build volume on a printer and the requirements to get nice rigid motion go up exponentially. I used 9mm wide gt2 belts because I was worried that 6mm would not be adequate, but I am sure the 6mm belts would do ok. There are steel reinforced 6mm gt2 belts out there somewhere. I can never find them. They are white not black so they are easy to spot if you feel the need to search for them. I have heard of people using them with great success if you can find them. A steel reinforced belt will not stretch nearly as much as the regular fiberglass reinforced belts we all use. A steel reinforced belt will also hold the tension better and require much less retentioning over the life of the belt.
Edit:Come to think of it, you should really look into finding some steel reinforced belts. Having dual direct drive extruders is going to be a heavy setup. That is a lot of mass to control and you will need very tight belts in order to get precise positioning.
Which brings me to my next point. I still get vibrations throuh my printers frame even when printing at lower speed 30-40mm/s. This has caused me to add bracing to my printer so I would strongly suggest you go nuts on bracing your printers frame, especailly so since you are running a dual extruder setup.
One last thing. Look into adding a reverse bowden setup if you are not planning so already. I use it on my coreXY and it works great.
What about a cloths pin spring? They are much stiffer. But then how do you pull the belt tight? Going to need a special clamp or something. Like those zip tie tighters.
You don’t like the lmuu bearings, I found some made out of derlin. They have less slop then the ball bearing ones. And its a self lubricating hard plastic.
Or have you looked at 8020 they have extruded aluminum that have a derlin pad that slides in the tslots. Thought about using that instead of the hiwin rails. Its cheaper and takes less parts, and provides the same function.
@NathanielStenzel @Kyle1 have either of you found closed loop steel belts? You guy’s have me concerned that my z axis closed loop belt drive system will not work good enough.
@Alex_Hayden I do not know where to find steel reinforced belts. I have heard others talk about steel reinforced belts. Maybe the http://openbuilds.com site?
Shouldn’t need a closed loop belt for the Z axis. You have to anchor the belt the Z axis carriage anyways so why not just anchor both ends of the open belt.
@Alex_Hayden come to think of it, why would you need closed belts? Just bind the two ends together and keep the belt bind point in a harmless location.
Found the steel belts. This seller also has 10mm wide steel belts and pulleys which is interesting…
6mm belt
10mm belt
ttps://http://www.aliexpress.com/store/product/PU-with-steel-core-GT2-belt-2GT-timing-belt-10mm-width-2m-a-pack-for-3d/1962255_32545925611.html
I don’t follow. How do you bind the belt? I don’t know how you would do this without making the belt skip at the bind point. Do you have an example? I am using closed loop to drive 4 tr8 speed screws in the corners. missing/deleted image from Google+
I think I must have confused you guys. This is the z axis belt. It loops around all 4 corners where it drives 4 tr8 speed screws. The belt has to be closed loop because it has to move continuously in one direction to move the bed up to the print head and then turn around and spin the other way to lower it while building the object. The yellow lines are the belt for z. missing/deleted image from Google+
This however will work for the XY axis. I can use a open loop and mount the ends to the print head. The yellow lines here are showing the XY belt. missing/deleted image from Google+
