Homemade Knockbox removable bottom for cleaning

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#1: Post by ldilts »

I made this Knockbox for $8.00 in materials easily obtainable from Home Depot. Its features are a removable bottom for easy dumping of pucks and sink cleanout. All materials are acrylic (Not PVC). They can be obtained at the sewer and drain section of the store, built in an afternoon; producing a knockbox that is both great looking (copper and brass), practical and strong.

The photos below show the knockbox full ready to go with the removable bottom in place. The second photo shows the unit with the bottom piece removed ready for dumping and cleanup. Purchase the outer ring (D-2852, D-3034 4" diameter, $0.79) and the bottom piece (it has louvers inside) $1.79). Also purchase a foot of 5/8" diameter clear tubing, 1ft of 1/2" copper pipe, (2) 1/2" copper end plugs, (2) 5/8" rubber groumets. Go to a hobby store and buy a sheet of brass (0.010 x 4 x 10) to cover the bottom louvered piece with. Pick up at HD, some JB weld, an epoxy 2 part glue that will glue the brass sheet to the bottom piece.

NOTE: the materials for the tube and bottom piece ARE NOT PVC!. The sewer section handles plastic that is made of acrylic, an easily carvable material, not brittle like PVC. I took a 3/4" spade bit to drill the holes for the 1/2"copper pipe. Go slow with the drilling. Acrylic heats up and melts easily. Once drilled take a knife and trim excess material from the holes. Insert the groumets. Lightly lubricate the inside of the groumets with vaseline where the copper tube will be pushed through. Cut copper tube with a hacksaw, insert the tube through the lubricated groumets and press fit the copper end caps on, lightly tapping with a plastic or rubber hammer. Cut the clear 5/8" tubing to length to fit the inside. Take a razor blade and slit the length of the tubing (one side only). This allows you to open the tube up slipping it on the copper pipe. It also allows easy removal for cleaning (although grounds have never worked their way under the tube). It is best to use fine sandpaper and "rough up" the brass sheet and the bottom piece before putting the JB Weld on. That way the brass will adhere to the bottom better. Place the louvered brass sheet on a table and trace the bottom piece around it. Use old scissors to cut the brass sheet. Mix up JB Weld and using a wooden match stick, LIGHTLY place the glue on the bottom outside perimeter and louvers. Press the cutout brass sheet on the bottom, place something heavy on the bottom piece and let dry overnight. JB Weld is waterproof when dry. I put some sticky foam tape on the N and S poles(outside) to give a snugger fit on the bottom piece. When emptying, push with your finger on the bottom piece and it will pop out ready for dumping. I used a saber saw with a thin blade to cut the opening out on the front to accommodate the portafilter handle. When sawing this out, set the speed on the saw at the lowest setting, if not, as you cut the acrylic at high speeds, it melts forming a weld behind the blade. If you are good with a coping saw, that would also work, but I can't figure these saws out. For the cutout, I drew with a compass a 4" circle and taped that on the front of the top piece and traced around it with a permanent marker. Be careful and don't cut below the ring on the outer tube that supports the bottom piece! Acrylic does not coffee stain! I have had mine under the sink for a month (don't tell mamma) with pucks in it and merely ran it under water using my hand to rid it of coffee stains. By the way, I have used this 60 times with no failure. Acrylic seems to "bend" with stress, versus PVC which fractures.

Home Baristas, Feel free to use this for your personal use, HOWEVER commercial vendors be forewarned! This is copyright and patent applied for protected!!!!

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#2: Post by jesawdy »

Nice! Looks a lot like the Grindenstein.

Anybody know of if acrylic can take a paint? If so, what kind?

BTW, Welcome to HB!
Jeff Sawdy

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#3: Post by espressme »

jesawdy wrote:Nice! Looks a lot like the Grindenstein.

Anybody know of if acrylic can take a paint? If so, what kind?
BTW, Welcome to HB!
Hi Folks,
This info may be out of date but it used to work for me.

All Acrylic can take paint. Clean the plastic well, wipe with a top quality mineral spirits and dry. A good cheap primer is spray can "Bondo® primer in very light coats " Duplicolor®" truck paints are darn near bulletproof over clean plastic and light primer coats."

If spraying with a gun, for one coat of color use lacquer with a bit ( tablespoon to quart pot)of MEK. That makes the real stick tight welding with surface used for second surface and top surface. Try on scraps to find amount of MEK and time for "flash off" between passes.

Krylon® is bragging up their new spray can thermoplastic stuff too. I have not used it.

Same technique for polycarbonate, styrenes, and most "white" PVC Piping.
Almost nothing works on Nylon, delrin, polyethylene, polypropylene, or slippery plastics.

I'll take this time to say GREAT JOB on the knock box!! I want one..Men's Mall here I come!

Best regards to all!

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#4: Post by bill »

I had a new knock box on my Christmas list but Santa didn't come thru. Seeing what you've built makes me think I came out okay after all. Off to Home Depot!

I wasn't born in Texas, but got here as fast as I could!

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#5: Post by mogogear »

I was just in the paint section the other day- There was specific spray paint for plastics. It was designed for people to repaint resin outdoor furniture!! I can't speak for it- but does the Depot stock a black version of what you have made?

Also a section of black heater hose over the copper pipe might makeless stainable deadener :idea:

All in all a very nice project----! :) well done!!!!!
greg moore

LMWDP #067

ldilts (original poster)

#6: Post by ldilts (original poster) replying to mogogear »

I did not see black acrylic pipe when I was there, just white. I use the clear acquarium tubing over the copper pipe because I wanted the nice copper color of the tube to show through. The clear tubing doesn't coffee stain despite over 60 uses so far. When the tubing starts to scratch and gets beat up (about 40 uses), I just cut another one; the the unit looks brand new. Black heater hose would hide the aesthetics, but it is personal choice. The resin paint sounds cool but I can't seem to paint anything without runs. The white acrylic is nice because it doesn't coffee stain. Cheers.

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#7: Post by RegulatorJohnson »

how bout a steam table pan from a restaraunt supply store.

some threaded rod. some nuts and washers.

a length of automotive fuel line hose for padding?

here is what mine looks like.


if you buy from chris coffee you get the wooden frame.

if you make it yourself no frame.

2012 BGA SW region rep. Roaster@cognoscenti LA


#8: Post by 2xlp »

its not even a wood frame. its a plastic frame made to look like wood.

its also an AWFUL fit. i was rather disappointed at spending $20 on a bad fit like that. i wrote chris, and he replied they were all like that after checking a few boxes, bad mfg. thankfully he only charges $20 for it, while some other vendors ask $40.

i 'fixed' it by stacking and gluing a layered sponge, then gluing it into the wells on the casing, and carving out a tight fitting for the bolts. its super secure now. i only needed: a sponge, shoo goo, and a pair of scissors

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#9: Post by RegulatorJohnson »

i wrapped a few rubber bands around mine...it is a $20 POS no doubt. :D

2012 BGA SW region rep. Roaster@cognoscenti LA

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#10: Post by oofnik »

I think this is my next project. I like it a lot.
I never figured out why a box with a padded bar going across cost $40 anyway! :shock: