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Jobro

I wanted to make a version of this Jobo motor base with a direct drive instead of a pulley system.

I had a spare motor and parts left over from the last version, so I’m making another one so I can keep the current one in use. The shaft was easy to turn down, but motor itself was a pain to mount with the right angle drive transfer and the wire terminals sticking off at an odd angle. I made an enclosure out of 6mm ABS, then cut a hole the diameter of the motor out of an ABS panel sized to the ID of the enclosure, then cut the panel in half to make a cradle for the motor. The back of the drive transfer case had a mounting bracket built in, so I made a clamp out of a 1.5″ aluminum block with a mortise cut in one side to house the bracket. It’s pinned through the center of the bracket with a bolt, which allows a little radial motor adjustment to make sure the shaft is level. The aluminum block it attached to the ABS base from below. It would be better to make this mounting block out of some sort of plastic- the aluminum is essentially a tuning fork and amplifies the noise of the gears, I’m going to redo that at some point.

The shaft coupling is Delrin. The OD is stepped to provide a little splash guard for the enclosure. Both shafts are a pretty tight fit in the coupling, but I installed some nylon-tipped set screws just in case. Once coupled to the motor shaft, I shimmed the drive shaft level and parallel to a flat surface, then measured the height to the bottom of the bearings, then made some mounting rails to that height. The rails are sections of aluminum channel mounted on round aluminum spacers. The spacers have two notches cut on top to fit inside the channel. I rounded the ends of the channels to clean up the appearance a bit and soften the edges a bit. The bearings are mounted to the channel, but since the channel wall is too thin for a decent thread, I made a simple mounting plate for each bearing that fits in the channel, just a short piece of 1/8″ bar stock tapped with two holes at the same bolt spacing.

The ABS enclosure is barely big enough for both the motor and the PWM board. I’d planned to put the board and controls in a separate enclosure but it just fit over the motor transfer case. I just had to file down the plastic fin at the top of the transfer case and make some threaded spacers out of stainless steel rod.

All the edges of the ABS box are rabbeted to interlock, which made solvent welding the box easier. I used Acetone in a hypodermic applicator with a very small bore, about 0.5mm. I was going to use some ABS cement, but that stuff is thick and messy, so I tested the Acetone on some scrap and it worked pretty well. I taped the box together with blue tape as shown above (without the top of course). The motor cradle pieces were positioned to the bottom panel with double-stick tape. Satisfied it was square and the lid still fit well in both directions, I ran a tiny bead of Acetone down each inside seam.

The switch and potentiometer will get mounted in the enclosure lid. The base will be ABS as well (piece shown not yet cut to final size), with some adjustable feet for easy leveling on my sloped sink. The 6mm ABS may be too thin for the base, it’s pretty flexible. Once the rails and enclosure are attached it might be more rigid.

The shafts will have 25mm diameter neoprene wheels, the Jobo drum is about 208mm across, so it’s roughly a 8:1 drive ratio. The motor turns full speed at about 200 rpm, so that’s about 25 rpm at the drum itself. That’s the fastest speed I’ve been using on the pulley version, but with the combination of pulleys I have the motor PWM needed to be dialed way back for such a slow rotation. I was worried this might shorten the life of the motor over time, so it’ll be good to use the motor at full power.

February 18

To finish I made a support for the leveling feet and to reinforce the base, then the shafts were installed with the neoprene wheels and nylon bushings on the ends. The neoprene was a pain. The bore was undersized for the 8mm shafts, so opened it up by using a progression of drill bits fed in by hand with no power. No good way to clamp the rubber, too spongy, so just held them in hand. Once bored out, I used a drop of liquid soap to help push them on the shafts. When the rollers in place I thought I was done, but the bore was no longer concentric. During a test run the Jobo drum danced around quite a bit. I installed the wheels between centers on the lathe, using one of the shafts as a mandrel, and trued them back up with really light passes. The carbide tool did not leave a good finish on the neoprene, but the texture does make them quite a bit more grippy than the burnished factory surface. They’re still not perfect- the mere act of pushing them on the shaft deforms them a little, but maybe they’ll relax over time. If not I’ll put them back on the lathe in their installed positions on the shaft and turn them down a little more.

 

Made some leg support rails with what I had on hand, helped make the base more rigid. It’s 1/2″ (OD) aluminum channel with solid 1/2″ blocks at the corners for the leveling feet thread.

Shop-made aluminum feet with a Delrin cap on the bottom to keep from scuffing up the sink bottom. The leveling feet have a 1/4-20 thread tapped into each of the solid corner blocks, and will accommodate a 1/2″ per foot sink slope. Each foot has a nylon jamb nut to lock the setting in place.

A little goofy looking, but it works. I like that it can be used in either direction, the previous version had the controls in front, so with the giant pulley on the left end it could only be used with the drum facing right. With the control box on the side, this one can be flipped for use in either direction.

Leveled for use

February 20th

Of course when I went to test it the DPDT reversing switch failed. I had a spare available from a weaker version of the same PWM board, so that was a pretty easy fix. I had been wondering when the switch would fail, it had suffered through a lot of reversing cycles over the past several years.

I made some different shaft rollers as well. The neoprene was too easily deformed and just wouldn’t run true. Unable to locate any stock shaft rollers that weren’t $20 a piece and unwilling to experiment with every type of rubber round stock that McMaster Carr sells, I just made some from 1″Delrin with some O rings fit into a shallow groove. This increased the OD of the rollers to about 32mm, which also increased the top speed to about 30 revolutions per minute.  The O rings will also be much easier to replace if they get worn out or damaged. The Delrin was press fit onto the shafts, using a little soap as lubricant. A 5/16″ (7.9375 mm) drill bit for the 8mm shaft made for a pretty tight interference fit, no set screws needed.

I should put some screws in the enclosure lid, but the fit is pretty tight so might wait on that. The walls of the box are pretty thin for screws, will probably have to glue in some corner gussets first.

Delrin shaft rollers with O-rings. I’ve since cut these in half, there’s no need for them to be so wide. There’s plenty of drive friction with a single O-ring per roller.

The nice thing about the plastic ‘extreme misalignment’ bearings (source below) is they swivel inside the pillow blocks, so the shafts can be installed or taken off without taking everything apart. I also made sure to space the bearing rails far enough apart so the rollers can be installed on the shafts before assembly, which made taking the shafts on and off for these little tweaks much easier.

Sources:

8mm Bearings: https://www.mcmaster.com/#6687k33/=1bm39mh

8mm stainless steel shafts and ABS sheets: https://www.servocity.com/

Neoprene roller material: https://www.mcmaster.com/#8637k121/=1bm7ye6

PWM board: (currently unavailable, I used a 150 watt board, a 200w would be a better match for the motor) https://www.amazon.com/gp/product/B00HTZ5OS2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

12VDC Motor: http://www.amazon.com/gp/product/B005IR1NBA/ref=ox_sc_sfl_title_6?ie=UTF8&psc=1&smid=AZRTOP7JJB0T8

The Delrin and aluminum stock as well as most of the raw materials and screws are from McMaster Carr, except for the aluminum channel and nylon jamb nuts which were available locally.

A few final tweaks. I rounded over the inside ends of leg blocks, then trimmed the width of the base and radius’d those corners as well. Didn’t like the sharp corners. Also re-made the motor mounting block out of ABS, but that didn’t reduce the noise of the gears much. The original timing belt version of this is a bit quieter, mostly due to the lower RPM of the motor. The gears in the direct drive version do add some noise and vibration as well, even though they’re nylon and packed with white lithium grease.

 

March 13th

As mentioned, the gears in the motor on the new version are relatively loud, enough so that I’m making a few modifications to the old pulley version. I guess I’ll have a  spare if one ever fails.

New parts from stuff on hand. I made a stepped shaft extension, with a female end to cap the odd little worm drive shaft on the motor and a male end for mounting the drive pulley.
Of the shelf, the conduit opening in this 1.5″ Cantex box isn’t quite big enough for the motor, so the hole needs to be bored out a little. This also means that the bottom of the box has to be carved out about 1/16″ for the motor to sit level.  Originally I did all this with a small sanding drum and chisel. The bore was half-decent, but I cleaned up the chiseled mess on the bottom with a 2″ face mill. I cut the recess longer than the motor for room to inset an aluminum bracket to help locate the motor position and to hold it in place. To attach the motor I drill a few holes through this and bolt it to the tray below. (This is a Type LB conduit body, which also had a conduit union in the bottom that I had to hack off flush with the box. Cantex sells a type E box with only the single union on the end but I couldn’t find one locally. I just covered the hole in the bottom with some rubber gasket material, which helps absorb motor vibration.)
A stepped Delrin cap fits into the enclosure opening and was bored for the shaft coupling. The small brass spacers on the bottom right photo are to mount the PWM board. Since the board I used for this is no longer available, I ordered a slightly stronger version rated for 10A/ 200w. It appears to have the same dimensions, so hopefully the board standoff hardware will still fit [it did]

 

New old base, trimmed down a little from the previous version. Materials, base, shafts, pulleys, bearings, motor, and timing belt are the same. I did replace the printer feed rollers with .25″ ID x 1/8″ thick O-rings- much easier to install, very inexpensive to replace if needed, and widely available. I really liked the leveling feet on the ‘improved’ version, so made some for this one too. The Delrin caps were a little slippery on the other feet, so made a recess in the new ones to take stock 7/8″ rubber bumpers. The bearing mounting rails and motor tray are essentially the same as the old version, just made the corner mounting blocks bigger so I had enough space for the  screw thread on the leveling feet.