Multiple Layer MFT - Best Approach to Boring?

[onocoffee]

I'm making an additional workbench that's somewhat in the style of the Paulk SmartBench with 20mm x 96mm dog holes but I would like to bore three matching panels. Perhaps I'm cheap or perhaps I strive for perfection, but I've been boring my MFT tops by hand - essentially, with a ruler and forstner bit.

Perhaps all the measuring is getting to me because I want to sandwich all three tops together and then bore the holes through the three tops - all at the same time. I'm just wondering what might be the best way to sandwich them all? Clamps? Screw them together (I'm irrationally concerned about holes)? Or double-sided tape them together?

Has anyone done something like this?

Thanks!

 

[Michael Kellough]

I'm making an additional workbench that's somewhat in the style of the Paulk SmartBench with 20mm x 96mm dog holes but I would like to bore three matching panels. Perhaps I'm cheap or perhaps I Istrive for perfection, but I've been boring my MFT tops by hand - essentially, with a ruler and forstner bit.

Perhaps all the measuring is getting to me because I want to sandwich all three tops together and then bore the holes through the three tops - all at the same time. I'm just wondering what might be the best way to sandwich them all? Clamps? Screw them together (I'm irrationally concerned about holes)? Or double-sided tape them together?

Has anyone done something like this?

Thanks!

Securing three sheets together is trivial. Just use clamps and if a clamp ends up in an inconvenient place and you can’t just move it over then replace it with a countersunk screw. But thats the least of the problems.

The bold statements don’t jive. If you’re really “concerned about holes” you should be using some kind of jig to locate them and then only bore one layer at a time, with something (like a router) that will keep the holes pretty perpendicular to the surface.

If you’re laying out the pattern of holes the old fashioned way and aiming at a mark with a bit then the way most folks do that is to put a 20mm Festool boring bit (8mm shank) in a Festool plunge router. But I doubt even a Festool plunge router has precise enough plunge action so that the bottom sheet will match the top sheet perfectly.

So, what most people do is make one perfect version then clamp it on top of another blank panel and use a top bearing router bit to “copy” the holes into the blank. Various ways have been used to make a rough hole in the blank to get the router bit into position.

 

[Cheese]

If your aim is to just create an MFT with 20mm holes scattered helter-skelter across the top surface then go forth.  [smile]

However, if your aim is to create a 20mm hole pattern that is both 96mm on center and each hole is perpendicular to the next, then a fixture of some sort is mandatory. It's just nigh-on impossible to create that perfect form by individually measuring and marking each hole location, prospecting for gold in your driveway would yield better results.  [smile]

Like Michael said, you need to use a fixture to ensure the holes are drilled at the proper interval and at the proper location. After that, we can then discuss the centerline perpendicularity issues.

 

[PaulMarcel]

When I wanted an MFT-top for my other non-MFT bench, I asked a local guy to CNC it. It was perfect and the cost was negligible since, as he said, the pattern was the simplest to setup. Another benefit for me: his MDF was high-grade imported Canadian stuff I can't buy (he bought by pallets) and he let me take all the off-cut scrap I wanted that he had by the house. Overall, it was a steal

 

[onocoffee]

Thanks for the thoughts. I appreciate them!

I ended up sandwiching the three plywood layers together with just clamps. Worked fairly fine. The grid I plotted on the surface of the top layer by hand, with a pencil and ruler. 20x96. I've done it this way for all of the MFT type boards I've made recently - and while certainly not perfect (sometimes very not perfect), it's been very workable.

This started originally when I wanted to dog hole my old workbench, but since I thought that would be a one-off project never to be done again, I decided not to get the UJK Parfit Guide due to the additional expense for a one-time use. However, since that mod it feels like I've been drilling 20mm dog holes into everything. Now, it's more of a challenge to see just what level of precision I might be able to achieve by hand.

After striking the lines, I bored the holes with a Fisch 20mm brad point bit, which has a length that would go through all three sheets. The plywood was from 4x8 sheets that were left sitting out in the elements for the past ten months outside my friends shop. Not in perfect condition but solid enough for a shop project.

I thought it went well enough but wrapped things up near midnight last night, so this morning when I go back in, I'll be able to see just how bad it is in the stark light of day.

 

[Tom the Remodeler]

I agree with the above statements, if you're striving for perfection, you'll be best served hiring a local CNC shop to fabricate the tops.

If you want to bore them by hand, then you'll want the UJK Part Guide System, drilling one panel at a time.

Stacking the panels increases the likelihood of compound error. Many users here struggle with getting an exact grid on a single layer, adding depth will exaggerate any imperfection in your setup.

All of the above assumes you're using the 20mm hole grid for squaring/aligning purposes. If you just want a grid of 20mm dog holes for miscellaneous clamping, then some clamps and a 20mm brad point bit in a drill guide will get you some perforated tops very quickly.

Good luck, and safe woodworking  [smile]

 

[MikeGE]

When I wanted to make my MFT-style workbench, I considered having the top made by a local shop with large CNC capabilities.  The owner understood what I wanted, but told me he could not guarantee the accuracy of the grid pattern at the end of the 2-meter length.  He made smaller replacement tops for some of his customers, but did not make the larger top that I wanted. 

I bought the UJK Parf Guide system, and don't have any regrets.  The cost of the UJK system was about the same cost of a one-time job at the CNC shop, but now I have unlimited use of the system.  Also, the grid pattern on my 1 x 2 meter worktop (200 holes) is accurate, as best as I can measure with my tools.

 

[Packard]

A couple of points:

I’ve made three work tables with MFT-style tops.  In each case, I screwed a piece of pegboard down on a slightly oversize sheet of MDF, taped off the holes I did not want to drill, and used a vix bit to drill the locator holes. 

I then used a long bushing mounted on a 6” x 6” sheet of 3/4” ply and proceeded to drill.

In each case there was one hole that was out of alignment.  In each case it was at a different position on the table top.  And I was never able to figure out how the deviation occurred.  The deviation was probably just under 1/16”, but still noticeable.  Maybe a PARF jig would have avoided that.  I don’t know.  I reviewed my process and I could not find the answer.  I have the miscreant hole outlined with a magic marker.  I am always able to work around that issue.

The second point was that I used a long bushing (about 1-1/4” long) and I drilled the required hole in the plywood using my drill press to assure that the holes are square to the sheet.

If you are off by 1/2 degree in a single sheet of MDF, that means the start of the hole and the end of the hole is .750” and the half degree angle is insignificant. 

But stack the sheets 3 high, and that 1/2 degree deviation from 90 degrees will yield an error that is 3 times as large.  The angle deviation will be the same for all three sheets, but the location of the third sheet’s holes will be off (someone will have to do the math for me).

The deviation will be even greater if you mistakenly flip one of the sheets over (the top sheet or the bottom sheet. 

Also, my drill got pretty warm drilling out the holes.  Drilling out MDF holes 3 times the thickness will create more heat.  (I used a 110 volt corded drill).

Note:  I do wonder how many home produced table tops maintained perfect alignment.  I ran a straight edge along the tangents of a line of holes.  In all cases one hole  on the entire sheet showed an alignment issue.  I never read a post where someone has tested similarly, so I am wondering . . . [big grin]

 

[jeffinsgf]

At the risk of encouraging inaccuracy  [eek], can I point out that if you are using the holes as designed by Festool (that is, as a clamping system), absolute precision is not necessary. If you're using the dog holes to align sheet goods, then all the posts suggesting CNC or Parf Jig are spot on.

 

[Packard]

I was originally planning on using the holes in the table top to hold face frames for assembly.

I found it easier to make a jig that drops onto the MFT-style top.  The jig has a fixed 90 degree angle built into it.  I just have to drop it onto a pair of holes on the table top.