Author Topic: MFT box beams with 80/20  (Read 1728 times)

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Offline Jruks

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MFT box beams with 80/20
« on: May 08, 2019, 10:39 AM »
Unfortunately didn’t take a ton of pics during construction and can take more of the finished product if folks want, but wanted to throw this design out there.

It’s a combo of an MFT with @fritter63 ‘s version of Josh Finn’s box beams. I modified dimensions of each beam  to be 5” total height and 15” total width and 6.5feet total length.

Theyre made of 1/2” AC ply throughout and I added a sacrificial 1/4” mdf top (held in place with some screws and carpet tape (which made drilling the holes a pain...) since I didn’t want the top moving as I was drilling holes.

Finished the sacrificial mdf too with 3 coats of dewaxed shellac.

Added 80/20 3034-light extrusion on all sides to allow for mounting jigs, connecting the two beams and keeping them in line, mounting things like router table etc between the beams, dog hole extensions to allow me to cut wider than the table, and plenty of other things I can’t think of yet.

Cut out between the webbing on the bottom to allow me to reach under and screw things in from the bottom.

Added a bunch of offset holes via parf guide mark 2 system so my cut marks don’t go through dog holes since I plan to use dogs to square the track.
« Last Edit: May 08, 2019, 11:01 AM by Jruks »

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Offline TSO Products

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Re: MFT box beams with 80/20
« Reply #1 on: May 08, 2019, 12:02 PM »
very practical approach. Workmanlike construction. Did I miss pictures of your box beam construction? wonder what you would do different next time?

Hans
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Offline Jruks

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Re: MFT box beams with 80/20
« Reply #2 on: May 08, 2019, 03:40 PM »
very practical approach. Workmanlike construction. Did I miss pictures of your box beam construction? wonder what you would do different next time?

Hans

Thanks! Was pretty utilitarian in this build :). Nothing gonna get finished but the replaceable/sacrificial top, which was done with shellac.

I’ll dog for other construction pics but I did this in about 3 days and didn’t stop to document it much unfortunately. My hands were too tired from drilling so many holes :).

Only two things I’d do differently so far -
1. I’d route shallow dados and grooves to accept the four walls into the top and bottom faces. 1/2” ply was too flimsy and a pain to get and keep square along 6.5 foot length. The grooves and dados would solve this by giving the walls a place to fit.

2. I’d attach the sacrificial top with screws only even if that meant putting some in strategic places on the bench. I used carpet tape through out the face and it was a nightmare to drill the dog holes through. Besides it gumming up the drill bits it made inserting and taking out the guide pins a hassle not worth dealing with. I originally decided to go this route because I wanted firm contact between the sacrificial top while drilling all the holes. Not sure it was worth it...

Offline Jruks

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Re: MFT box beams with 80/20
« Reply #3 on: May 14, 2019, 07:26 PM »
Just an update. Put the bench to use for the first time this weekend and it works great. Allows for super wide cross cuts and rips as needed and is quite easy to keep the grid aligned (with the help of two alignment jigs consisting colinear holes made with the parf system - a long dead straight edge would also work but I find the jig is easier to align both ends quickly with one pair of hands).

I added a rip/crosscut fence made with the original incra jig purchased from lee valley, along with 3ft of their Veritas quad track rail and 2 flip stops, and a couple pieces of 3/4 mdf. It sits on a base with a grid of MFT holes as well so I can move it around the table since it only has 7” of travel. It was fairly easier to square up to my MFT hole pattern but I found the fence flexing if I put too much off axis pressure on it. Right now I am using a Veritas wonder dog to apply a touch of pressure behind the edge of the fence closest to my cross cut rail and that resists and off axis flexing just fine. I’ll likely  beef up the fence or make a new one out of 80/20 in the future if it turns out messing with the wonder dog becomes annoying - it def would for production work but I’m a hobbyist mostly.