MFT as an assembly table

[tarpon2007]

Recently I went to use my MFT 1080 as an assembly surface for gluing up some small (17"x20") mitered mirror frames.  During dryfit of the clamping setup (bandclamp and corner blocks) I noticed that the frame was not sitting flush on the MFT tabletop and if forced to sit flush, the miters would open slightly.  As I had been quite careful with the miters and their bisquited reinforcement, I rechecked everything, including the frame member flatness, and the table flatness.  The MFT tabletop was dished considerably, about 1/8" along the long dimension, and somewhat less on the transverse dimension.  I also checked my other two tables (another 1080 and an 800).  Both were also slightly dished, with the smaller ( and newer) 800 almost flat (dished about 1/32")  I guess I shouldn't have been surprised, after all, the tops are just a plate of 18mm MDF supported around their edges, and MDF is not particularly stiff.

I had known that the aluminum frame members were not reliably perpendicular to the top, but I had hoped to use the top as a reliably flat assembly surface.  Bottom line is that you need to check all your tools for accuracy if you want to do accurate work.

Fix for the top's lack of flatness is easy, I built a grid of straight and stiff 1"x 3" maple strips and screwed the top to them, forcing the MDF back into flatness.  I used #12 brass screws, countersunk slightly into the top, and didn't glue the top down to the strips so I can flop it over later to use the other side.  The strips (two lengthwise, and two transverse) are located so as to not block any of the dog holes.  3" wide is about as much as you can go w/o interfering with the legs foldup.  Does the fix add weight?  'Fraid so..

 

[alg]

MDF is very porous. There are threads here where others have sealed both sides of the top. I need to get-around to sealing mine.

 

[joraft]

Fix for the top's lack of flatness is easy, I built a grid of straight and stiff 1"x 3" maple strips and screwed the top to them, forcing the MDF back into flatness.  I used #12 brass screws, countersunk slightly into the top, and didn't glue the top down to the strips so I can flop it over later to use the other side.  The strips (two lengthwise, and two transverse) are located so as to not block any of the dog holes.  3" wide is about as much as you can go w/o interfering with the legs foldup.  Does the fix add weight?  'Fraid so..

You've come up with a great solution for the problem, the only possible negative being the extra weight attached to the table. And thanks for alerting me to something I should have thought of, but didn't. Maybe that's because my MFTs are still fairly new.

I've got several tables connected together, and as much as I like the setup, it takes up a lot of space. After seeing the great mobile bases with storage some of the members here have built, I've been mulling over and sketching some ideas for building something of my own. You've got me thinking that I might want to incorporate a small adjustable support under the center of each table, small enough to fit between the holes. If the table is flat, the support could be adjusted with only enough tension to keep it that way, and if it should sag a little, it could be adjusted with more tension to bring it back to flat. I imagine that the sagging is a gradual process (less gradual if the table sits with a lot of weight on it), and occurs where the table is parked most. So, when I do use the table off the mobile base for short periods there should be no need for the extra weight of a stiffening grid.

John

 

[Paul Perry]

I'd also like to thank you for your post and your suggested fix.

I was lucky with my first MFT (a 1080), the MDF top is flat and the sides are perpendicular to the flat top. It was only upon receiving my second (an MFT 800) that I found out how lucky I was, the 800 being a completely different story with non perpendicular sides and a "dished" top.

 

[John Stevens]

the only possible negative being the extra weight attached to the table.

This type of reinforcement is a must on a "jumbo mft," so I've done it a few times.  Today I picked up some pauwlonia from a local sawmill for this purpose--it's dimensionally stable, and although it's not as strong ash (another wood that's dimensionally stable) as it's reasonably strong and extremely light.

Also for what it's worth, if you "scallop" the top edge of the stringers a bit so they only touch the bottom of the table at the mid-points between the holes, you don't have to worry about clearance for the clamps.

Hope this helps.

Regards,

John