Trying a McWire RepStrap

HI all,

Just thought I would drop a line and let everyone see that I've finally gotten started on my own RepStrap after having snooped around here for these past three or four months.

The pictures below show what I have done. I've made mention over in the General Forum about the new bearings I'm using instead of the stand-alone type mentioned in the original McWire bot build.

I did all of the work with a pair of pliers and a cordless drill. No what you would call accurate but with a little extra time to do measuring and placing correctly you can get good results. My rails line up almost perfectly as far as I can tell with my limited equipment.

I bought a 42" by 24" sheet of 1/4 inch plexyglass for the stages. I'll be cutting that shortly after I make certain that I have the dimensions down right. That stuff is expensive and I don't want to mess it up!

As I don't have a shop or even a work-bench (I live in an apartment) I had to do all this on the floor of our small kitchen. My girlfriend is very understanding! I used wooden stakes as spacers between the floor and my drill bit and for lining holes up on the frame's tubes. Worked wonderfully.

The spacers between my rails and my frame are there so that the 1/4-20 bolts don't stick out above the top of the rail. Works well and and is very steady. There is very little slack in the setup even without the nuts on the bolts.

All in all I'm very pleased with how things went. Any comments or suggestions would be greatly appreciated.

Cheers!

I have done much the same. As of today both X,Y stages are complete with opto end stops. My extruder is already built and tested so what remains is building the Z stage and working out the kinks. I am guessing that I have another 2 days of solid work before I start laying down HDPE. I am still waiting for an adequate solution to the extruder temperature problems. I think Adrian's work is an improvement at the temperatures that are needed for CAPA, but the higher temperatures for HDPE don't seem to be controlled very well even with the new code.
Second order bugs I have noticed is that once a stepper is activated the 298 gets very hot even when the stage is no longer active. This tells me that we are keeping both sets of coils energized. This is probably not a good idea. I tried 1/4 ID tygon tubing as a coupler between the motor and the threaded rod, this did not work well. 7/32 rubber Windshield washer tubing works great. I bought some 1/4" fuel line but the OD is to large for my setup. Pictures are much like yours.
After I get Z and the extruder working I am planning to re-implement the Y end stop as it currently limits the Total travel in Y by ~ 1/2 inch. Working volume is ~ 9X6X6. I used self drilling/tapping screws for the majority of the attach points. Countersunk 10/24 for the Attachment to the y stage (coupling nut, bearing bracket) and a threaded insert for the op-to interrupter blade.

Best,
Dan

I've been having trouble finding coupling tubing for my motor-threaded rod connection. I hadn't tried the auto parts stores yet. Windshield washer tubing sounds like a good idea. I've spent a lot of time in various hardware/home improvement stores looking for coupling ideas. I'll give the washer tubing a try.

I was wondering if there was a better/more elegant way to do the z-stage threaded rod assembly. It just seems sort of haphazard. Maybe its my inexperience but I think it could be done better/more simply.

Cheers

Looks good. I remember the joys of building things in an apartment. I bet my neighbors do too :-)

For the tubing, I think I did use 1/4"? ID tygon. I'm not sure about the size, but it screws onto the 1/4" rod if you use a lot of force. The motor shaft was smaller diameter, so I used some aquarium air tubing to step it down on that end. Not the easiest stuff to work with, but it seems to work ok so far.

Since steppers don't hold their position without power, we've got to keep them powered up even when the platform isn't moving. With a threaded rod drive, there's enough friction that there's little chance of this happening, but it's probably a different story with the belt drive. I know some systems idle at a lower torque setting, which is something we could do but don't.

I've been stuck on the extruder temperature readings for a while too, but Andreas' latest firmware is now working well for me. I think he's going to be posting a new revision in a day or two, so there may be a solution by the time you get back to messing with the extruder.

I am using orientalmotors Pk266 .9 degree steppers, (the ones I posted about some months back in the stepper motor thread). THey are very close in specs to the nanotecs. To get the stages to move I have the torque set at 75%. This is no doubt contributing to the high idle heat disipation on the stepper boards.

Good news on the temperature code. Are you paralleling the thermistor with a resistor to linearize the samples? What integrating cap and what rx is your thermistor. Mine is the Vishay 01T1002FP specified in the BOM rx is 32660.

hey guys!

awesome pics and progress. i have neglected to take pictures, but I also have gotten my x/y stages assembled and working. i'll take a bunch of pictures when i get to the lab tonight. also, theres a good chance that this design will be featured in a Make podcast, so keep your eyes peeled.

i've made a good # of improvements, and will have updated DXF plans here shortly. i'm very pleased with how well the mcwire style design is working out. here's a quick list of things i've modified:

* fixed skate bearings instead of aluminum rail for bearings (you still have 2 rails for each axis, but the 3rd U channel is replaced with two bearings)
* spring tensioned dual rollers on the other side (the spring brings them together and keeps the tension to make adjusting and attaching the slides super easy.
* horizontal bearings so the acrylic rides on skate bearings instead of directly on the aluminum rail. this TREMENDOUSLY reduced the friction. before, i could move the stages back and forth easily by hand, but now they literally *glide*. i can just give it a little push, and it will continue to roll, whereas aluminum on acrylic would stop when i stopped pushing it.

i'll be in the lab a bit this week, and then all of this weekend coming up. hopefully i can get the whole thing assembled and working. that would be an absolute dream. pictures coming!

I'm using much smaller motors, but probably about the same current draw. It gets hot, but I can still touch the heat sink without getting burned.

I'm using a 0.47uF capacitor with the 10K thermistor from Futurlec (beta 3881,
Rz 32113) paralleled with a 470 ohm resistor. The 470R is probably unnecessary, I've tested the firmware with resistors up to 10K and it doesn't have any problems reading it directly. I think the resistor is a pretty elegant solution and it keeps the firmware from having to re-range several times, so I'll probably keep using it anyway.

BTW: the Futurlec thermistor isn't great for our purposes -- it's fairly big, so you can't get it completely buried in the acorn nut. It is also only designed for 125C, and I think I'll be in the 160C range for HDPE. So far it seems ok at those temperatures, but we'll see how long it lasts. I've got a glass bead one from for the next nozzle that looks much more appropriate.

Hi all,

I've scrounged four bipolar steppers--four wires coming off them, right?--from two printers that my family had laying around. I'm planning on using them but they are different step sizes. Two are 200 the other two are 400. I'm assuming this can be dealt with in code but some assurance would be nice.

Also, I didn't like the coupling nut design that they had for the Mcwire--seemed shoddy--so I'm welding my coupling nuts to 1/8 or 1/16 strips of mild steal from our university welding shop. I'll drill holes in either side and and mount them that way. Should be okay. I'll counter sink the holes so they are flush with the stage on top. Want this to look nice. Pics coming soon!

Also, Zach, what's the ETA on the next round of extruder kits? I didn't get in on the first round cause I figured that there were other people who would put them to better use for the community than I could. Sounds like the second round will be mold-cast. Sounds good to me, how much and when? (not to be pushy, I'm only excited!) ;-)

Demented

Demented Chihuahua Wrote:
-------------------------------------------------------
> Two are
> 200 the other two are 400. I'm assuming this can
> be dealt with in code but some assurance would be
> nice.

It can. In the preferences dialog, you specify how many steps it takes to move the extruder 1mm. There are three settings, one per axis. There are also independent torque settings for each.

I had no idea they put 400 step motors in printers, sounds like a great find.

> Also, I didn't like the coupling nut design that
> they had for the Mcwire--seemed shoddy--so I'm
> welding my coupling nuts to 1/8 or 1/16 strips of
> mild steal from our university welding shop. I'll
> drill holes in either side and and mount them that
> way. Should be okay. I'll counter sink the holes
> so they are flush with the stage on top. Want this
> to look nice. Pics coming soon!

i havent had any problems with the coupling nut... other than that you cant tighten it down too much or the nut gets slightly compressed and there is lots of friction on the drive rod... who knew?

>
> Also, Zach, what's the ETA on the next round of
> extruder kits? I didn't get in on the first round
> cause I figured that there were other people who
> would put them to better use for the community
> than I could. Sounds like the second round will be
> mold-cast. Sounds good to me, how much and when?
> (not to be pushy, I'm only excited!) ;-)
>

i'm getting my molds in the mail here in a few days. i'm going to try my hand at molding some extruders, but i may also pass them on to Luis Freeman if he has more time. Also, Ian Atkins in the UK is making me some batches, so we'll have some coming up soon.

i'm not 100% sure on the price yet, but the raw materials seem to be around $10 / extruder, so that + the other parts (heater, nichrome, PTFE, screws, etc) + a little bit for labor will probably put it under $40 / kit. i'd say that halving the cost for an extruder kit is pretty awesome!

Zach,

That's awsome! I was only hoping for a $20 decrease in price. Anything even close to $40/kit would be a real steal. I may just be too excited for this though! ;-)

Cheers!