Monday, April 26, 2010

Assembly Update #2

Just a quick update without pictures. This weekend I managed to complete all the parts for the x axis. I cut out all three opto flags, drilled out the x bar spacers and then completed the assembly of the vertical-bearing-360 as well as the motor mount. I was thrilled that the 360 bearing fit perfectly on a steel bar at the first trial fitting. Much better than the x-carriage which still needs adjustment to clamp the bar correctly.

I then started working on the assembly of the x axis and immediately had trouble. The biggest problem is that the holes for the bars do not line up correctly. from measuring the x axis carriage I can see that the bars need to be about 5cm apart. The spacing of the holes on the various parts varies from 4cm to 5.5cm. This means that I have to go back to my trusty Xacto knife and Dremel to adjust them. I hope to have the full x-axis assembly assembled tonight or tomorrow.

When attempting to install the first stepper motor I found that there was some kind of mount already installed on the motor with a pair of screws. These have proved to be extremely difficult to remove and I am afraid that they have permanent threadlock on them. I have tried a couple of things that have not worked and my next step may be to heat them up with my soldering iron in an attempt to defeat the threadlock. Hopefully I don't also defeat the motor itself!

There were several ebay auctions for full parts sets for a "Wade" style geared extruder. Given that the geared extruders have a better reputation for reliability, I decided to go to one of those right away. The extruder parts from the cast set are a bit rough anyway. I managed to win the auction and the parts should be here within a week or so since they are actually coming from Toronto, right here in Canada.

I should also comment on a post that I made a while back. I was going to order some of the trickier parts from Provantage to avoid having to adjust the cast ones. Although they were very helpful and prompt in their communications it turns out that Provantage does not ship to Canada (or anywhere internationally) unless you are buying the full set of Mendel parts ($1500!!!)

I guess I will continue with my "Hack it with sharp objects until it fits" method for the time being.

Monday, April 19, 2010

Powder Printer Recipes

Powder printers, which lay down a thin layer of powder and then use a binder fluid to bond the object together, are now being built by the home hobbyist community. One of the factors limiting their usefulness is the powder being used as raw material.

Most commercial printers use proprietary materials in their print beds and they tend to be very expensive. Now that people are building their own machines there is a lot of interest in developing cheaper materials that can be created at home. There are a number of recipes for different powders out there for use in diy powder type printers. A lot of them, and the best of them, come from Open3dP (Open 3d Printing) at the university of Washington, though there are also a few others that I have seen on various forums.

I have collected as many of them as I have encountered in a single document which I am making available to anyone who might be interested. There is nothing revolutionary about this document. I will just save you the time of looking back through all the blog articles if you are trying to remember a formula. As time goes on I expect many people to be experimenting with different materials and I will update this document as I discover new information.

None of these recipes are my own. They are all the result of hard work done by other, smarter people so I can't answer any questions about them. Until I get a powder printer built I am not even able to try them myself. There is a lot of additional information available on the open3d site. That site is maintained by Professor Mark Gantor who has been very helpful in creating this document. Thanks to him especially for advising on how copyrights and proper credit should be handled. The Open3dP site should be the first stop for anyone experimenting with materials for powder printing.

For what it's worth, I offer this up to the powder printing community. The information is all in the public domain but the pictures are copyrighted by Professor Gantor. If you want to use the text in other documents please give proper credit to the original creators. The recipe book is in MS Word format and can be found here.

Assembly update #1

Made some excellent progress on the x-axis this weekend. I only get about an hour at a time to work on the Mendel, due to the ongoing demands of my actual life, so it is going slowly. Especially since there are a lot of adjustments with an exacto knife and dremel required to make the parts fit properly.

X-Carriage with bearings aligned properly

I managed to fix the alignment problem that I had with one of the bearings on the x-carriage and then proceeded to construct the idler bracket and the vertical bearing 180. There are still some adjustments required because I can't align the bars as it stands at the moment. I will need to adjust the holes in the vertical bearing so they line up better.

Two shots of the Idler Bracket

Vertical bearing 180 (very rough parts, will need major adjustment with sharp things)

It was obvious that the cast gears that came with my RP parts are completely unusable so I posted a request on the Reprap Mechanics forum and discovered that Markus Amsler offers free Mendel gears for just the cost of shipping. A quick email and my gears are now on the way for the unbeatable price of $3.80. Markus is in Europe and he didn't specify the currency so I sent it in Euros, still only about $5.00 Canadian and well worth the price. Thanks Markus!!

I will post a picture of the crap gears along with the new ones when they arrive.

When assembling the idler bracket I discovered that the 4mm fender washers that I bought are exactly the same diameter as the bearings so they will not work to constrain the x-axis belt. I went to Canadian Tire (my favorite store) and picked up a handful of 6mm fender washers which worked just fine. I also finally bought a set of metric hex wrenches to make assembly easier.

4mm washer on the right. Too small. Larger 6mm washer on the left. Just Right!

The opto flags need to be installed as you assemble the x-axis carriage and the vertical bearing so I will have to cut them out before proceeding further. I tried to print out the template last night but couldn't get the scale right. I will try again today and will probably use HeeksCad, which was conveniently blogged about by Niel Underwood over at RepRap Log Phase. It looks like it would be able to match the dimensions on the dxf file to the printer to get the scale right. We'll See. I did get a start on this task by buying a six pack of coke and drinking several, so can report that I have made progress.

I have been having some trouble with the camera so I haven't posted any pictures for a while. I finally asked my daughter. Since she is a teenager she is, by definition, much smarter than me. She pointed out that the old camera that I was trying to use was crap, I have started borrowing her, most excellent, camera for these shots.

Sam the Science Dog

By the way, here is a picture of my assistant. Sam recognizes that I require constant supervision to keep from severing an artery with an exacto knife so he sleeps beside my workbench. Also, when I start throwing parts that don't fit, he brings them back.

Monday, April 12, 2010

Assembly Begins!

It has taken a while but I have finally started construction of the Mendel. Definitely a very exciting day.

On Saturday, I went out to the garage and cut all the smooth and threaded bar stock for the machine. It took about an hour and a half. I bought stainless for the smooth bars and I went through two hacksaw blades cutting it. I smoothed out the ends of those on the grinder and I was ready to go. I actually still have to go out and cut the three jigs because I forgot about them at the time but, I will cut them as I need them.

My Molded Parts

The molded set of RP parts I bought from Ireland are extremely rough. The holes are all undersized, probably due to shrinkage in the mold material, and have to be drilled out. If the shrinkage in the rubber caused undersized holes it also probably caused the entire part to be slightly oversized. Many of the holes were filled with a rubbery substance and others were completely filled in with the casting material. I finally realized that parts of the rubber mold had broken off in the bolt holes when the parts were removed from the mold. The missing holes are where the bits broke off in the previous casting and were not present during the molding of my parts. This would indicate that the quality of these cast parts drops significantly from the first casting onwards. There is also some warping but not enough to cause problems

Anyone buying these cast parts should inquire whether they came from the first or second casting from a particular set of molds. Anything after that is suspect. Whoever bought the set that was cast after mine probably had most of the holes completely filled. I would not recommend these cast parts unless you can acquire them for considerably less than a set of printed ones. They require much more manual cleanup to be usable.


I started by cleaning up and drilling out the parts for the carriage assembly. The x-carriage upper and lower parts have a lot of trapped nuts and some of them needed to be enlarged or cleaned up with a Dremmel in order to get the nuts into them. The majority of them were OK, however, and a bit of pressure with a set of pliers allowed me to force fit the nuts into their cavities.

Strangely enough, my most serious problem was that I don't have any metric hex wrenches. None of my SAE ones would fit well enough for even rough work. I had to grip the cap of the screw with a set of pliers since they require more torque than I was able to apply with fingers alone. I will pick up a set of metric hexes this week.
My most serious problem was that one of the holes for the bearings on the lower carriage was missing and I drilled it at the wrong angle. You can see from the pictures that the bearing outlined in red will not sit correctly on the steel bar. I am going to have to remove this one and redrill the hole.

In the end, however, I was able to assemble the very first parts of my Mendel. I can see that the assembly will take quite a bit longer using these cast parts but they should all prove to be usable. I will certainly make printing a proper set of replacement parts a high priority as soon as the machine is operational though.