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| PeterE:
Throwing myself into this thread ... This is an interesting read! I have also started to look for a potential 3D printer for my other hobby (Model Railroading in 1:87 -H0 scale). A fair bit of items lend themselves to be made using this kind of printer. I have found that the setup I am most appealed by is closest to a Prusa i3 Rework version with a plywood box frame. The box frame is very stable in Y-direction and fairly stable in X-direction. This can be seen from this image where a plate is used: http://reprap.org/wiki/File:Prusa_Box.jpg The original Prusa up till i2 (iteration 2) was set up like a triangular frame in which the moving axes are fitted: http://www.emakershop.com/browse/listing?l=717 This frame is more stable in X than in Y direction. What I would like to do is to make a Prusa i3 Reworked (latest version) using a plywood box frame and brace it with diagonal bars front and back. I think that would make for a very stable setup in all directions. Then, if the whole thing is secured to a base plate of something like 25 mm ply, that would be as stable as it can get and still be possible to make in a modest home shop. In all other parts the base i3 stuff works nicely as a start. What are your opinions on these thoughts? BR /Peter |
| picclock:
Hi PeterF These are my thoughts on the Prusa i3 so far. For me plywood is not stiff enough, nor dimensionally stable (humidity and heat are the worst offenders), hence my choice of a metal frame. The weak point in the i3 mechanical design is maintaining the right angle/positioning between the X/Z axis and the Y axis. I have a 600mm square granite kitchen worktop which I will use as a base. By mounting the Y frame directly to the base and using side supports for the gantry, also mounted to the base (as per the plywood version), the stiffness and precision in all three axis will be maximised. By using a direct filament feed to the hot end the loads on the x axis are varied with the need to unwind filament from the spool, additionally the mass of the x axis is increased by having a stepper motor attached. So my choice will be to use a bowden feeder system. This may be iffy for very flexible filaments but for Nylon/abs/polycarbonate it will give better results. The X axis tensioner is either not implemented or pulls against the vertical smooth rod. I will alter this to place the tensioning load on the two horizontal X axis parallel rods. Will initially assemble mine with M5 stainless studding for Z axis and test the results. If accuracy is nbg will replace with better system. Am also not happy with running two stepper motors in parallel from one driver chip so may well make an adapter to use two driver boards, one for each z motor. Any mechanical mods I make will be probably machined out of aluminium to preserve accuracy - plastic has too high a temperature coefficient for precision stuff. Future thoughts :- Stepper motors, the Ramps board uses A4988 chips which are rated up to 35V. Unlike most things, turning up the voltage on a stepper driver results in a decrease in average current consumption and allows a much higher stepper speed - so this is something I may investigate. Likewise an increase in heated bed voltage will allow speedier warmup. Much better Ramps Heater FET needed for this trick. Obviously, plus side of heater bed just goes to higher voltage supply. Hope to order my kit in the next week or so :ddb: Best Regards picclock |
| PeterE:
Hi picclock, Thanks for feedback! Much appreciated! About the plywood. The box version of the i3 suggests 12 mm furniture (multilayer) ply and that I agree with, but I would double the thickness on the upright frame for both stability and better meat for screws. Also, to improve the X-Z vs Y stiffness, I will add a diagonal bar from the table surface to the top of the frame. This of course requires a sort of table surface and I have a suitable old piece of 40 mm chipboard countertop. Cutting that in suitable dimensions and then sealing the edges will make for a good enough humidity-resistant base for the whole thing to begin with. I think it will be sufficent to stabilize the printer and maintain accuracy in print. The vertical Z axis studding will use stainless for me too. 5mm seems to be standard so that it will be. No ball-screws yet. I will still keep the combined drive for two stepper motors from one output to begin with. Then when it comes to filament feed and other things, they will be dealt with as the build goes and usage experience tells. Your future thoughts sounds very interesting so I will keep looking in to this thread. A friend is currently printing the plastic parts on his machine as we speak. BR /Peter |
| picclock:
Hi PeterE After some further investigation yesterday, I have decided to build from scratch rather that a kit. The kits are more expensive and still don't have the parts or support the configuration I would prefer to use. So I have started to order parts from ebay and will do a build thread in the project logs when I get started. One of the changes I think is fairly important for a good machine is to change the stepper driver chip to the DRV8825 flavour. I have designed pcb's with the a4988 and I know from experience how ratty they can be at 1/16th step. The DRV chip will microstep to 1/32, but more importantly is a smoother driver, with a higher current rating. I ordered 6 assembled, Ramps compatible boards from ebay at £1.32 each last night. Does your plastic printing friend take orders ? A lot of the frame parts/bearing holders I will make from Aluminium, but there are some bits like the extruder and the motor holders I will struggle with. I can get a complete set for £36 but will probably not need half of them. Good luck with your printer project. It sounds like you have the right ideas re stiffness. Best Regards picclock |
| PeterE:
Your suggestion on using DRV8825 stepper drivers sounds like a good choice. I will though stick with the currently common a4988 ones at the moment as I have a fairly steep learning curve to do before getting fluant here. What was the name of the RAMPS compatible boards, they sound as if they are good valy? I can check with my friend if he can provide some prints, but don't wait as this is done within the company I work for if you know what I mean. Sounds like I too should make some photos too when I get started. BR /Peter |
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