Hex Coupling Nuts as bushings?

A friend of mine, who's recently also caught the RepRap bug, was looking for bushings to use with the 8mm rod. With access to a lathe, he reamed out some Hex Coupling Nuts, using an 8mm reamer, and gave me some to try. The process was quick and the result was excellent!

With 8mm centre removed what's interesting is that a sliver of thread groove remains inside. We figure this would serve well to retain some light lubricant.

It's a lovely fit and a very smooth movement.

I've fitted a pair to my X-Axis just 'cause! I'm begining to think the extruder platform might actually be stable enough with only two of these... they are such a good fit!

Motors and electronics ordered...

Quick update: I've ordered Gen6 electronics and motors today. I'll continue to investigate extruder designs and only move on parts for that once I've chosen a design I like. I plan to experiment with extruder variations once I have a functioning chassis.

Thank you for visiting! Feel free to leave a comment.

The Print Platform...

This week I gave time to the print platform construction, reviewing images, approaches and discussions on the topic. The basic Prusa Mendel style print platform is a two tier structure. The lower smaller board has bushings attached and rides on the parallel rods of the Y-axis. The upper board is typically square (225mm) and held aloft by springs on four bolts, and usually carries some kind of heated bed.

The debate continues on-line about the purpose and merits of the spring platform arrangment, and even about the number of supporting bolts to use. The springs are to allow easy levelling, and possibly absorbe accidental impact of the extruder head. The argument in favour of three bolts instead of four is that you can more easily level the platfurm with three spring loaded bolts vs four. I'd agree with this but would thing the down-side is a larger section of the square platform is now unsupported and may flex depending on the rigidity of your platform material.

I'm not sure of the need to have any leveling capability at all though. If your rods are alligned on the horizontal plane, and parallel to each other, your Z axis accurately perpendicular to the horizontal, and your X axis perpendicular to Y, then why are you levelling the platform? Surely you should get the Y axis right and step the 'print platform' up to the desired height with fixed height rigid risers from the Y-axis bushings.

For me, the four bolts with springs design will do to get started, but I've beefed up the bolts and springs. I'm choosing a 'mushroom head square neck' bolt which secure nicely and have a low-profile. I could have gotten away with 5mm bolts but had some 6mm to hand.

Here's my construction method including the attachment of the bushings... Time will tell how well it works!

The upper and lower boards were clamped together and four holes drilled. The positioning of these holes isn't actually critical. Just mark the boards so you can assemble in the same orientation as you drilled. The round holes were then squared out with a needle file to receive the bolt neck.

To position the bushings accurately I put two scrap lengths of wood together and drilled two 8mm holes in them at the desired distance apart for the Y rods. This is an easy way to get the holes perfectly alligned. I then temporarily fit the bushings and rods as per the photo.

 I used Araldite 2 part epoxy to secure the bushings to the under-side of the base platform, allowing it to set over night.

I then fitted the bolts to the top platform, first squeezing them home with a wing-nut for convenience, then fitting a washer and nut and a dab of thread lock.

Finally, I fitted the springs, attached the top plate to the base plate and secured it with some nylock-nuts.

That's it for now!

Got some 8mm Stainless Rod for X and Y...

This week... I found a local supplier of stainless steel, and bought a 3m length of 8mm stainless rod (Good value round these parts at €6). They only sell in full lengths. I cut new X and Y axis rods. The stainless was easier than I thought to cut even by hand with a hacksaw. Mark the desired length carefully and grip the rod in a vice, protecting the rod from the vice jaws.
Once cut it's a good idea to round off any sharp edges with a flat file.

Since I'm using bushings rather than bearings I though it would be good idea to polish up the stainless rod. I gave it a rub with Autosol and then used the drill and an old rag to polish off. Stainless polishes up nicely!

I had got 8mm mild steel rod first and it served will for mock-up purposes, but the finish was poor. I'am now going to swap it out with the stainless on X and Y.

As I've been reading through the RepRap site there's constant reference to X, Y and Z axis. I did a sketch and kept it near 'til I got the hang of it! Might be of use to someone! :-)

Either end of X...

I had some 6mm rod around, and found the center bushing from an old set of rollerblades fitted the rod nicely (I'm saving the rollerblade bearings for later). Now, I do suspect the 6mm rod would be much too light for use in the Y or X axis, but in a vertical direction (Z) I just might get away with it.

With my self-imposed material choice constraints (wood), I reviewed the existing plastic design for the 'x-end-motor' and 'x-end-idler', and simplified it to two basic parts per end. I did a dimensioned sketch (below) before cutting anything. I haven't figured how best to secure the motor or idler yet but will return to that, but I think the motor will incorporate relatively easily to my design.

The x-axis and all belonging to it, is raised and lower by threaded rods passing through captured nuts in the x-ends. The Prusa design incorporates a spring between the captured nuts (see here) to keep the nuts tensioned on the threaded rod, reducing rattle or back-lash. I'm going to try a long-nut instead of this. There's little or no play in a long-nut, especially if the threads are lightly greased, and with the thread in a vertical direction I don't expect any back-lash problems.

(Ignore the motor in the pict. It's an old 5.25" drive motor, It's been good to get a sense of scale until I order a set. If anyone has used these old motors successfully in a reprap then do let me know.)

Here's some picts showing my construction of the X-Ends.

The large and small pieces are cut, and carefully glued as per the diagram. I've also drilled two 8mm holes (60mm between centres) in the base before assebly. These will receive the x-axis rods, but I haven't finalised a method to secure them in place.

The verticle block was screwed as well as glued to the base. It's not going anywhere!

Once the glue set, I drilled an 8mm hole through the vertical block, and sunk a 14mm hole in the base to take the long M8 nut.

The nut will be epoxied in. The bushings push nicely into the top and bottom of the 8mm hole to receive the 6mm rod. secured in with a dab of pva.

Here's both X-Ends loosley assembled on either end of a pair of 8mm rods.

There's clearly a lot more detail to be addressed, such as securing the x-rods, mounting the motor and idler, and bedding the long-nut in epoxy.

What has occurred to me though now having got this far, is that the whole thing might work better 'upside-down'. It would give more free area for mounting the motor/idler and the the long-nut would be pushing the assembly rather than pulling it! (see pict below)

Two steps forward...

When I get so far with measuring and cutting, it's hard to resist a little bit of building! I know it's a waste of time to start construction until you have all the bits, but it's hard to resist! :)

I got some 8mm rod over the weekend and cut it to size. I got enough rod-clamps made up to fit the Y-axis loosely, and then cut two Z-axis motor mounts, again from my trustee oak floor board. (I'm going with the Prusa variant, which uses two Z-axis motors.)

I'm probably going to route a square in Z-axis motor mounts to receive the motors, but I'll wait until I have motors to get the fit right. I'm debating how best to clamp the top of the Z-axis rod to the motor mount. For now I threaded the end of the rod and tapped the oak. Not the best I know but holds it for now. I might thread the top of the rod some more and fit lock-nuts above and below. We'll see...

So here you go... progress to date in pict below! Next it's how best to build the X-end-motor-mount and X-end-idler... out of wood. :)

Rod Clamps...

The Prusa Mendel has the simplist of rod clamps, a good improvement on the original Mendel design. But faced with which type of clamp I could make more easily with 'stuff' to hand, I reverted to mimic the original design.

I routed two 8mm slots, 8mm deep, in what was left of the oak floor board. It would have been better to use a round-nosed 8mm bit, but didn't have one to hand.

Back to the chop-saw to cut to length 35mm.

Rotate through 90Deg, push against the stop and cut again to square.

There you go! A hole in each corner to take a nut and bolt of choice and I have a set of clamps.

The Frame Vertex

The 'frame vertex', or what I might more loosely call those corners on the equilaterial triangles of the RepRap Mendel frame, is a lovely simple little joint. But, try find a dimensioned drawing that you can easily use to reproduce one of those joints in any other way than on a 3D printer! That's the whole point you might say!

Anyway, I eventually gave up looking and did my own 'old school' drawing, so I could make a template for my 'corners'. A good starting point.

I went with 60mm between centres, a whole number, as against the 58.??mm I've seen on some drawings. To me, this dimension isn't as critical, it's ensuring each piece is identical to the next that matters more. I didn't bother with all that chamfering either.

A template was marked out and cut from MDF.

Copies were marked and roughly cut out with a jig-saw.

The template was screwed to the rough 'oak blank'.

The blank was carefully matched to the template using a router with follow-bearing.

(Do not attempt this process unless you are very exeperienced with your power-tools and take full safety precautions.)

[Cutting the piece with a jig-shaw to match the drawing as accurately as possible will also suffice.] 

A hole to take the M8 threaded rod is drilled through the pilot holes.

Six vertices are bolted on two threaded bar off-cuts, the perpendicular holes marked as per the drawing, and drilled through.

Here is one Vertex test fitted.

I had concerns originally about the wood splitting, but with it now cut-out and assembled, the hardwood feels very solid. With it bolted from all sides everything seems to hold everything else.

Printer build under-way...

Greetings and welcome!
After reading up for the past few weeks on the whole 'RepRap' concept (http://www.reprap.org/), I took some time over the holidays to gather materials and devise an approach, a plan! This is just an initial post. I'll add more detail as things move along.

At this stage, it's probably more a RepStrap than a RepRap since I'm using wooden joints. But once under way, the plan is to replace wood with plastic, just for authenticity if nothing else. It's a real chicken 'n' egg though, and since I don't know anyone else with a RepRap and don't want to buy parts I could make, I've gone ahead and made a start.

The build is under-way, and good fun! :-)