I had a unique opportunity to build a flowbench. You are probably asking, what the heck is a flowbench and it doesn’t sound like furniture or a cabinet. Well stay tuned and I will explain

First, a flowbench is a device used to test cylinder heads. Specifically, it creates airflow and static pressure to push or pull air through a cylinder head and the amount of airflow can be measured to assess performance improvements. All in an effort to improve engine performance. There is a ton of information, and honestly, where I picked up most of my information, and the build plan, from this forum: http://www.flowbenchtech.com/.

Second, a flowbench is like a large, complicated cabinet. It has a number of different chambers or areas that make up the internals.

The Plan and Materials

The plan for this flowbench was purchased from the PTS forum (flowbenchtech), but was modified to fit 4 additional vacuum motors as well allow some extra space for around the motors themselves. I add 8 inches to the length and added about 5 or 6 inches to the fore-aft depth.

• The Materials
  • (4 1/2X) sheets of 3/4″ MDF
  • (5X) 8′ 2X4s
  • Half Sheet of 3/4″ Melamine
  • Half Sheet of 1/4″ hardboard
  • Scraps of 4/4 poplar for door edging
  • Scraps of 3/4″ Plywood for check valves
  • (2X) Gorilla construction adhesive
  • Many, Many screws #8 and #10 (1 1/4, 1 1/2, 2, 2 1/2 lengths)
  • 5/16 All Thread, T-Nuts, Washer, Nuts for hold down plates
  • 1/4-20″ all thread, 1/4-20 bolts of various lengths, threaded inserts, nuts, washer for baffle plates, access doors
  • 1/4-20 Cross Dowels (Barrel Nuts)
  • #10-24 (3/4″) bolts and threaded inserts for switch console
  • 1/4″ Aluminum Plate for Switch Console
  • 1/4″ Acrylic Sheet for Baffles
  • Primer and Paint
  • Piano Hinges
  • Bulb Seal from McMaster Carr for RH Panel 93085K91
• The below Items were purchased by customer
  • (12X) Vacuum Motors
  • (12X) 3″ PVC Caps and Scupper Valves
  • PTS hold Down Plates and orifice plates (hardware included)
  • Port Covers for LH side baffle access

YOUTUBE Video 1, 2, and 3

Breaking Down Parts

I am not going to go into a crazy amount of detail since the videos do a pretty good job of showing it all, but I will explain a bit of it for those wanting the written version

It all starts with the PTS plans and my cut list for each sheet of 3/4 plywood. Then I cut each sheet down to rough size. After, I find some common RIP sizes and set up my table saw for common dimensions.

First Assembly

The very first item to be sized and assembled is the selector assembly. It is the very center of the cabinet and dictates the other cabinet dimensions. At this stage everything is just screwed together since it will have to come back apart a number of time. The selector assembly is comprised of 2 pieces of melamine and a piece of hardboard. Then, that assembly requires the motor plate and a lower divider added to it.

Remaining Assembly and Cutting Process

The rest of the pieces are sized from the plan or from the first assembly. There are over 20 individual pieces to the flowbench, so I won’t walk through them all, but just share some pictures of the process

Some of the last pieces to be assembled were the top and front console. I should have cut the 45 degree cut in the vertical panels before hand, but was worried they would be inconsistent. So I cut them all at once.

Right Hand Access Panel and Doors

I spent a considerable amount of time on the RH side access panel. It first started with figuring out how to seal the door properly and get all the profiles worked out. Wooden strips hold down the bulb seal, then barrel nuts (cross dowels) are used to constrain the panel to the cabinet.

There are two other doors in this cabinet. One is the very front door that allows access to the slider plate and internal electronics. The second door was not in the original plan, but makes motor access a breeze.

Motor Mounting System

After getting all the exterior pieces sized and screwed into place, I tore everything back apart and cut the 45 degree chamfer as seen in the above picture, cut out the door openings, access hole openings, airflow openings, adding a ton of internal blocking, webbing due to high static pressure (100″ of water). After all of that, I tackled the motor plate(s).

The motor mounting system is comprised of 3 pieces. Motor Panel, Motor Registration Panel, Motor Hold Down Panel. On top of this, there is a bunch of 5/16″ hardware. It starts with laying out all the concentric hole locations in all three pieces. Then going to town with drills, hole saws, jig saws, routers, sanding. Then, I cut the motor hold down panel into separate consistent pieces. Essentially the motor sits inside the motor registration hole and gets pulled tight by the all-thread squeezing the hold down pieces into the back of the motor.

Top and Switch Panels

The top is made of 2 pieces of MDF glued together for a substantial work surface. The edge of the tops gets a 45 degree chamfer to mount the console panel. I predrilled a bunch of screw holes and then glued the two pieces together using screws to clamp it together.

After the top was dry, I cut out a recess for the orifice and hold-down plate with a temple and router. I also drilled some mounting holes and the large center hole.

Similar to the top, I had to mount the orifice hold down to the orifice plate and also drill the baffle standoffs in the orifice panel.

The hold down plates were purchased through PTS and were really well made.

The front console is going to house all of the controls for the vaccuum motors and likely some indicators or readouts. After fitting, and cutting the front console to size, I had to mount some 1/4″ aluminum to it.

I chose aluminum inserts because the electronics may change over time and it is much easier to replace the piece of aluminum with a new one and start over. Also, most switches won’t mount to a 3/4 thick panel. After building it, I could have used something a bit thinner than 1/4″. I wanted to recess the aluminum panels. So I made a quick template with MDF and pockets screws and got out my double sided tape and router. I created the recess, then used a jig saw to remove the rest of the center portion to leave a little shelf for the plate to sit on. I should note that the aluminum is slightly proud of the MDF to prevent things getting snagged on the MDF edge and tearing it/chipping it. Then, I drilled some holes through the aluminum and into the MDF. Then added #10-24 inserts.

Prep for Paint

At this stage, the cabinet parts are all cut to size and all the features have been added. So, I started to dis-assemble the cabinet into each component. I sanded every component with 150 grit paper and I glued all of my 2×2 bracing into place. I added chamfers and roudnovers where needed. Note, that the bottom edge of all the panels that touch the floor got a heavy 3/8 roundover. I forgot to do this before final assembly, but it would have been easier/better as piece parts.

Then, I sprayed a coat of primer on everything. Then, sanded and sprayed two coats of latex paint on all the internal surfaces. MDF is porous, so it has to be painted. If I did it again, I wouldn’t use latex paint since it made my internal door stick. I also wouldn’t use the BIN shellac primer. This is my second project where I had poor adhesion to the substrate in some areas. If a painter pyramid was there or I had to mask the area later, the tape would pull the paint and primer up together. Still on the hunt for that perfect primer.

Check Valves

This unit has 12 motors and 8 of them will be variable controlled and 4 will be on/off. So, when the 8 motors are running and a subset of 4 are on, there will be a path for the airflow to recirculate through the motors that are off. It will be the easiest path for the airflow to go from the high pressure side to low pressure side. So, we need to stop that from happening and a check valve is the method.

The advice on the PTS forum is to use scupper valves. It is a simple rubber flap that seals against a rubber gasket, primarily used on boats/water. I originally thought this was going to a breeze, but it was actually a bit of pain due to making wooden rings to mount the scupper valve to.

The valve needs something to screw into and I wasn’t going to trust the PVC alone. So, I had to make some wooden rings/donuts. I started by using a hole saw and cut a larger circle from a piece of plywood. Then used a smaller hole saw to drill out the center of the circle. I wish I could remember the exact sizes I used. The OD was just a bit smaller than the OD of the PVC caps and the ID was larger than the flap opening.

The scupper valve is inside the cap and screws go through the PVC into the wood rings. Note the black mark that indicates the flap “hinge” is pointing up. I used the gorilla adhesive to mount these. Since I didn’t know which 4 were the on/off, I did all 12.

Final Assembly

Finally, it is time to put it all together. I started on the workbench with the selector assembly. I used the construction adhesive in every joint and could use the squeeze out as sealant. For areas that didn’t have enough squeeze out, I used caulk. This thing has to be air-tight. After the selector assembly was assembled I moved to the furniture dollies. And landed the selector assembly on the base. Then I added the center divider and lower internal panel (under selector plate)

Since the motor area was wide open, I took this opportunity to install all 12 of the motors. Attached gasket to motor, installed all thread into holes, got motors into place, installed hold-down loosely. Then worked my way up the motor plate. Once all motors were loose installed, I came back and tightened up all the hold downs. In the below picture, the top right corner of the hold down system had to be later notched to fit around the top panel.

After the motors were installed, I just kept on adding panels, adhesive, and caulk. It went smoothly, since I think I had this thing apart and back together at least 5 times before final assembly making sure there was nothing preventing assembly. I was really concerned about my 2×2 bracing blocking the assembly process.

Everything fit really well except for the front console. It needed a fair amount of flushing up.

Final Prep and Paint

After assembly, I flushed up all the panels with a router and sander. Then I added roundovers to all the corners to prevent chipout/breakage after paint. Then it was time to fill any gaps, screw holes, imperfections, and add drywall compound to all the edges and roundovers.

After a couple rounds of gap filling and sanding, I applied a coat of primer to the outside again (STIX by INSL-X). Then I sprayed some paint and found some more gaps/holes, so I had to fill them and sand again. It is really hard to see these small gaps/bumps in white primer. As soon as the gray paint hits it…BAM, its all you can see.

After two more coats of paint, it was looking awesome. I let everything dry for two/three days and came back out to start assembling it back together. I think this took about two months start-to-finish.