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Ajohn

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About Ajohn

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  1. Nigel gave you some good advice Rick. Hope I have the right one but fringexp will allow you to play with the mirror rad and put errors where you want them to be or put another way allow you to minimise the work that needs to be done. The only catch really is the need at some point to but the knife edge pretty precisely on the mirror rad. John -
  2. I'm pretty happy about microstepping now and it's effects. Google comes up with a truth about microstepping web page at the top but I think it misses several important aspects and am more inclined to follow the comments in the links I posted. What I am still asking about is the steps per mm set in the software. Typical 3d printers might use a 2.5mm pitch belt and either 16 or 20T pulleys. along with 16x microstepping This results in either 40 or 32 steps per mm being set into the software. They are exact numbers. 8x microstepping would result in 20 or 16 and so on. Belt stretch might result in the need to change them slightly. Lead screws and other things that could be used would result in different numbers. I read a comment about some one using a 4 start leadscrew with a pitch of 8mm. With 16x microstepping that would need 400 entering. Gina uses drums and a type of fishing line called braid. That is likely to need an entirely different number of steps per mm. There are comments about suggesting that too high a pulse count in the software can cause the micro problems because it can't keep up so was wondering what people have used which they know works without any problem and also what type of drive it's used on - belt and pitch. screw and pitch or what ever. To few a number of steps in the software say 2 would limit the accuracy that is achievable as it could only position to 1/2mm which might ( big might, big joke really ) work out on an extruder if the build platform moved quickly enough. The software probably ties that relationship up anyway but again the numbers that can be set in the software and that will work are important. John -
  3. I had hoped some one would answer the steps per mm from the software end. I've read that too high a number can give the micro too much work to do. Looks to be dated info but leaves me wondering. I thought stinking fish when the power drop of with micro stepping was mentioned and thought that doesn't make much sense when the motor is rotating at some speed to produce a torque to drive something. The holding torque will drop off but that isn't what matters. The rotational torque does. 2 view on the subject http://www.designnews.com/document.asp?doc_id=221386 a pdf to download on the page with the images and http://www.geckodrive.com/microstep-full-step-torque John -
  4. There seems to be a number of extruder like the one I posted fitted to a number of printers, usually in Bowden mode. No gearing and the gear that drives the filament through is larger diameter than the usual ones in the geared extruders. It is shaped like a gear as well. I'd guess it can't handle more than 1.75mm but I suspect that will suite me. It's fitted with a 1.8amp nema 17. I can give it a try anyway. A while to go yet as some bits have to come from far away to keep the prices down - angle brackets for the frame material I will be using. I should have asked the question in another way as well. Typical steps per mm as far as the controller software is concerned. The axis and the extruder. John -
  5. A question I hope some one can answer. How effective is microstepping on the extruder and axis. What sort of level is usually set? I've got to the point where I need to tie down feed rates on all of the steppers so wonder how far microstepping can be reliably pushed? The extruder arrived today. Some other bits have to come from far away but at least it's a start. This one could be converted to boden if needed. It appears to be the latest greatest. Doh I seem to have attached the image and can't add it to the thread. John -
  6. Not sure I have looked at the right parts Neil - 8bit 20mHz and a lot of variants? John -
  7. I was thinking in terms of using a shelf going back into the case to support the horizontal gears Gina. Backing paper running down from that an also in the "pocket" formed by the shelf leaving all of the gearing visible. I suggested making the clock face a bit smaller to get round the lack of visibility in the area you indicated with arrow A. That might mean changes to the size of the case or it might not. As it's a visual thing hard to say. The shelf gets around having a slot and leaves everything visible. I'm no artist though. Just a humble engineer. Mmmm you would have to support the prawl from the top of the case. Maybe something printed ? John -
  8. I thought the volcano site might give more info on extruders but apart from offering up to 1.2mm even for 1.75mm filament little else. They do a 5:1 geared stepper but is seems to have rather low power for that sort of ratio. I wondered if it might be possible to use a screw feed to get more contact area. Length of bolt pressing on the filament but it would need a seriously long drive shaft to avoid having a sharp bend in the filament. Might be an idea for a bowden type as might a rubber wheel. I looked at the data on the other driver I mentioned. It's 2.5a peak, 1.8a rms but a lot depends on the heatsink. I'd guess 24v and a lower current than 1.8 amps would be a good idea. Some of the heatsink may be built into the pcb. The link I posted includes a stick on one as well but I wouldn't assume the full 2.5a could be used. The kit I mentioned that uses 4kg/cm stepper uses a gear on the extruder (Gregs but for 1.75mm). Reading the manual they suggest setting up the axis about 1/4 turn on the pot past the point where the steppers get stable after a move/move smoothly and that during prolonged printing they should get rather warm but not hot. Looks like it's supplied in the UK, £279 and includes everything including loaded firmware. They seem to have sold 4, good feed back and at the moment it's not relisted. Good build manual too. Arggggggggggg Picking bits for these is painful but the kit suggests I can go over the top on drivers and maybe even steppers so if it doesn't work out use them on something else. Not sure what though. John -
  9. I'm pretty sure that the stepper drivers are completely compatible with ramps. They are offered as an alternative. The spec might be a bit misleading as the part they use is rated at 1.8 amps rms. The 2.5 amps is peak and they might best be limited to 24v even though they will go higher. I managed to find a little bit more on the stepper motor ratings, from an RS data sheet. The 80C temperature rise is correct and it seems they are ok with an ambient temperature of -20 to 50C, I wouldn't want to touch one running at 130C though and would probably pass out if the ambient was 50C. I've been nosing about on what power the extruder needs. Only comment I have seen so far is 5kg cm / 0.5nm. That's nearly as much as the longer 60mm nema17 gives that I noticed on ebay. Just a bit more than a kit which I think is made up in the UK for reprap prusa. That uses 4kg cm 1.7 amps on everything. This is for 1.75mm and I assume the usual nozzle size. Not sure about 3mm and larger but have seen comments that the 1.75mm can be sent through quicker. Think that was from a Chinese retailer. John -
  10. That's interesting Gina. When I looked at steppers the 12v ones didn't show up. I need more details on the electronics but my impression is that the stepper drivers are plugged into ramps so it's possible to use drivers such as these which allow the drive voltage to be increased which will also increase the speed the motors can switch at. http://ooznest.co.uk/3D-Printer-Electronic-Parts/Boards/DRV8825-Stepper-Motor-Driver These could be used for instance to switch 36 or 40v into the 12v parts which in principle will speed up the switching. I tried to find an online calculator that includes the effect of the series resistance as well as the inductance. No joy but 36v should cause them to switch state in under 600uSec. That's to a full 0.4A on a 12v part with a resistance of 30ohms and an inductance of 37mh. The time constant of the inductance and resistance 1.23mSec, twice as long. That's to a current level of 1/4 amp, it's = about 66% of V/R. A 1/4 amp with 36v would be faster than 350uSec. The times are to when full torque would be reached. I'm not sure if this matters on a 3d printer but it generally does on cnc which usually means use the highest possible drive voltage. The drivers regulate the current in the steppers. I'm a bit bugged by the ratings of the steppers. I looked at some industrial spec's and they mention numbers associated with an 80C temperature rise which would burn them out unless they were in a freezer. A 1/4 amp in a 0.4amp part would cause the temperature to rise by 0.25*80/0.4=50C and the torque figures will reduce by the same amount. Only problem is that there used to be these 1/2w resistors at work that they couldn't use so help yourself. Later I bought some of ebay and wondered why they got hot. I did think they looked a bit small but later found industrial ratings are roughly 1/2 the commercial ones so can be used at the ratings on the can. No more smoke now. I'd hope they didn't use a similar factor on steppers. Hope them quick sums are correct but the principle is valid. John -
  11. Thank's Gina The reason for thinking 23's one X and Y is that the X will be carrying 2 steppers and the guide and bearings for the X axis. Also in my view the same unit should from a reasonable basis for an engraver / super light router/miller. When ever this is mentioned on the web people compare it with cnc millers driven by mach 3 which in my view constitutes missing the point. They also mention missing G codes. At the moment there is a lot of work going on in various places using Arduino for cnc on lathes so why not mills. Initially I thought drive current to the steppers might be a problem but then found out how the steppers seem to be spec'd - 80C temperature rise. Often the case with electronic items, use the spec max's and things will let the smoke out. I need to check that area a bit more thoroughly. I wondered about 12v steppers as from memory they generally have more power but loose out on speed unless the drive voltage is much higher and in practice will probable never match the usual 2 or 3v parts. Not at all sure if this matters. Some one on another forum has a commercial unit that uses V rails. Initially they used an eccentric mounting on the wheels for adjustment. It seems that they caused problems and have switched to a rather stiff flat spring mounting which according to the owner is a lot better. In the same area something in the dim and distant past rings bells. I'll use 4 wheels not 3. I'm sure I have come across something similar where 3 didn't work out - down to very slight varying curvature on the rails. The rails for the frame work are a bit expensive but the fittings, corner blocks etc are stupidly so. Like £6 each for top corner 3 way joints. T nuts 60p a piece. My £100 ebay freebee looked like it would easily cover the lot till those cropped up - excluding electronics. Looks like we may have cross posted again - or maybe the site doesn't like my browser as there doesn't seem to be anothe post no I have submitted it. John -
  12. Maybe a smaller dial just showing the teeth of the larger gear and the rest of the drive sitting on a shelf hidden by the background. The case would probably look better oblong then rather than square. I nearly suggested larger gears to keep the dial the same but the case would still probably look better oblong. John -
  13. For some reason I can get rid of the quote. Took 3 days to read the long one. Interesting again. From this and the other my vision looks like it will involve a sturdy frame. Not sure which aluminium section to use yet. Comparing prices may as well be the V guide type but not sure yet. Expensive option but I had a weird Ebay refund recently and they didn't want the item returned and I managed to sell it. Be good to spend it on something useful. So it's looking like a 500mm cubic frame with space for bits at the bottom and a 300x200 build area and what happens to be left or less for Z. X at the top and Y on the table as I suspect long runs of braid or belt may be a problem. I'm still inclined to feed the Z from the X axis which might balance up the masses on x and y and use nema 23's for those. I noticed the need for gearing on the extruder so not sure about 17's. Any thoughts welcome. I wont be able to print anything until it nearly finished. One question Gina. How do the bought and the home made compare now ? Also I think I noticed one with the usual linear guides around still? I'm surprised no one has come up with an engraver based around ramps. John -
  14. I'm bleary eyed from reading the Pilot thread. A useful thread Gina. I'm worried. I now know I can buy some things such as borosilicate sheet etc. The braid is very abrasive so can understand why you switched to the V groove bearings. One of the interesting aspects was different masses on the x and y axis. I wonder if different motor powers might help - crazy thought. Good thoughts on the reasons for problems as well. I had forgot something that I actually spent some time using long ago. A drawing board. My excuse is that it was a different type but the x arrangement might prove useful. Not so sure about the clever twin axis one. Dose of optrex and a rest and I'll take in the other one. John -
  15. Thanks Gina. I didn't think to search extrusion. I think I am going to have a vision. I've looked at various kits and it seems to be a good frame and by the look of it missing parts on the electronic side, and may not be in the uk really or so so simple flat aluminium plate frame with everything that looks like it may be made by a UK company with all of the fittings printed. So in some ways making one up appeals. I found some details on how the braid is handled - clockwise and anticlockwise around a drum. I sea fish a lot at times so am bound to have some braid about. I've seen comments about it stretching but would have thought that would be pretty slight once the filaments in it have settled down. As timing belt is likely to have something similar in that may stretch a bit anyway. In some ways I would be inclined to use a typical router style set up for the z axis and also do all of the movements at the top. Trouble is that this wouldn't minimise the weights being moved about and the front back movement would need driving on both side really. Needs some thought but I feel I would only really need 100mm or so Z axis. The other axis are more of a problem as I don't really know but more than 200mm in one direction would probably be best. I've cross posted with you but will still submit this one. Whoops seems I didn't but the forum thought I had John -
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