AVL DIY : Making a Second Back Beam

How we got here

AVL 24 Harness A-Series Loom

A couple years ago, pre-pandemic, we bought a 24 Harness 40″ AVL A-Series loom from its previous owner on Long Island. It came with 2 x 1/2 yard sectional warp beams. After we got home and assembled it that we realized that it was missing the bottom back beam. We didn’t worry too much about it because we were spending most of our time repairing water damage and getting it up and running. Then, just about the time we were ready to start warping it, everything shut down. At that point it wasn’t vital that we had a second back beam because there wasn’t much to do.

Recently however we have been starting to get going again. We put a towel warp on to fill some orders from holiday shows and start weaving a new line. After we filled the existing orders we re-threaded the loom for the new run of towels. When sampling for new towels it became clear that the warp had to be set significantly tighter due to a structure change.

The solution was to use the second warp beam to add the extra warp. But what would we do without a second back beam? For the time being we ran the second warp up and over the existing back beam (image below). It wasn’t elegant but it worked for sampling and we knew that it wouldn’t work for production. It was time to get a second back beam.

Making a back beam to fit

Printing a test plug
Dry fitting the final plug
Plug epoxied in place
Plug design iterations.

While Tegan worked away at weaving and finishing the samples, I figured out the proper size round tube we would need. We got extremely lucky finding a version of it in stock at the local Metal Supermarket. What we needed for our loom was a 2.25″ outside diameter round tube. Metal supermarket has all sorts of round tube in different materials and wall thicknesses. In our case they only had thick wall tube in stock, so we took it, but it’s not necessary if you can find something thinner. It ended up costing us ~$45 for the tube cut to length (43″).

Once back to the studio we were able to take measurements of the tube and pre-drilled holes in the loom. I used these measurements to design a plug for both ends of the tube. Note that this is an older style AVL A-Series loom so the back beams do not easily pop in and out like they do on the newer versions. My original plan was to make a setup like the newer style, but ultimately decided to match the loom. That meant matching plugs to fit the pre-drilled holes on the loom.

Once I took the measurements I started with a quick and dirty 3D model of the plug to make sure my measurements were accurate. This allowed me to make sure it both the tube and the holes on the loom. From there I began refining the design making minor adjustments each time I printed it. Four iterations later I got the correct dimensions for a nice snug fit.

Once the design was finalized I used gorilla 2 part epoxy to secure the plugs into the tubing. When epoxying the plug in place I put the epoxy around the outer rim of the plug and slid it ever so carefully into the end of the tube. Once it was in and lined up I coated the face of the plug and the end of the tube with epoxy. I did this so it would hold in place better and it would create a smooth surface once hardened.

Then we waited 24 hours for the epoxy to cure and harden…

A Meme of Pablo Escobar Waiting...

Putting the back beam in place

Cured & hardened epoxy
Dressed for sampling
Back in business!

When ready we loosened the bolts on the top back cross support on the AVL, leaving the bolts just inside the nuts, and spread the verticals apart just enough to sneak the new back beam in. Kaboom! We have a second back beam.

For this warp we will simply cut and retie ends on the bottom beam line them up with the top beam. After this warp is finished, the top beam will hold the entire body of the weaving leaving the selvedge threads for the bottom allowing for independent take-up. This allows the weft to beat evenly in the selvedges.

The whole process took about 48 hours to complete. We had to get the tube, design and printing the plugs, and wait for the epoxy to dry. We got lucky considering all of the supply chain issues going on and how long it can take to get simple things for the business these days. It was quick work and let us keep chugging along on the project without major interruption.

Fixing a flaw in my design

As some of you, more versed in 3D printing than I, may know structural rigidity of a print is impacted to some degree by the type and amount of infill used. When I printed the plugs for the back beam I used the standard 20% diamond infill. This, ultimately, caused the print to fail when under the pressure of the warp and the weight of the beam itself for a period of time. When it broke I was surprised that it failed, but when I investigated what happened and thought about how to fix it, I realized that it was amazing how long it lasted.

I got to work drilling out the space where the peg snapped off and shaping new metal ends for the plugs as you can see in the phots above. I glued these in place the same way I glued the plug in place previously and let them dry.

In Conclusion

If I was going to do this again, I have two ideas for how I could do it better. One of them being to print a plug with a pre-determined hole size and use a threaded rod on each end of the beam in place of the smooth ones shown above. The idea would be to screw it in covered in glue with a smooth ground nipple to place in the loom. This would just give more surface area for the glue to bond with a bit of a tighter fit.

The second idea would be that I get one long center rod and run it the full length of the beam with rounded ends. I would put the printed plugs on the center rod and get it all in place before I glued it up for extra rigidity and support. If this was the path I took I may even add an extra plug mid way through the beam in order to keep the long rod more stable inside it.