MFT table top type of work - custom

[Brad Shipton]

Cutting out these holes on a CNC is not that complicated, but I do agree you need to add a tolerance spec to the diameter callout for circles on your drawing. The tolerance should read 20mm -0.000" / +0.010" (assuming the exact diameter of the MFT dogs is 20mm). If you put a spec like that on the drawing and they ask what that is, go to someone else. Anyone with Biesse, CR Onsrud, Thermwood or another of the industrial machines can produce a ridiculously simple piece like this to a tolerance of 0.005". If you need better than that you are working with the wrong media. If you start talking to someone with a hobby machine you will need to make sure they understand the capability of their machine. I could produce this on my 4'x8' machine to within 0.010", but that takes time and the interest in setting up your machine to do so when you buy an entry level machine (grid squares in image below all within 0.010" so I can use vacuum pods).

I think Ted means an oblong hole. That will be largely the result of a sloppy operator that never checks the X/Y accuracy of his machine. So long as they use a 3/8" diameter bit, and the machine is not a cheap pile, using a pocket tool path is fine. If you spec that you want them to use a special bit they do not own, they will charge for that. A 20mm bit will be in the realm of $100 and they may need a $30 collet as well. Keep in mind you will be begging for someone to do this. Someone that owns a $100k machine could care less about your $100. The less annoying you are the more likely they will do it.

If you could live with a reduction in the length that will make the operators setup a bit quicker. To utilize the full 60" length without much extra setup time they would need popup pins. Most cab shops have that, but some of the smaller machines do not. Also, you can probably get two for very little cost. If it were me, I would charge you for the full sheet of Baltic Birch unless I had a piece kicking around.

Shipton_CNC-Table-exx.jpg

[Keith Hankins]

I made my whole cnc 4x8 mft top so i could reuse my festool clams. You can also acomplish by making a jig and getting a forstner bit and do it that way.

[Ted Derryberry]

I actually meant a tapered hole that is tighter at the bottom than it is at the top. My machine isn't so out of square that a 3/4" diameter hole is noticeably oblong! I don't even start to notice anything being oblong until I get to a 24" diameter circle and then it's within "sanding tolerances".

I was "drilling" using 1/2" bit on a spiral ramp to create a 3/4" hole through 1" MDF and 3/4" cabinet birch plywood. By the time it got through the bottom of the plywood the machine/router motor (not a spindle)/bit were flexing enough that it was trying to stay in the center of the hole. I couldn't get any of my dog clamps to fit and had to chase all the holes with a forstner bit. Now I know better and have a long 3/4" bit. Someone with less experience might be tempted to try the same thing in lieu of buying a 20mm bit, which I suspect is a little harder to find and more expensive than a 3/4".

In short there are two issues that could easily come up with a hobby machine and/or inexperienced operator. Out of square pattern and out of spec holes.

I agree the biggest issue is going to be finding someone with the proper machine that cares about a small job. The guy willing to take on the small job is less likely to have the machine capable of doing it well and the guy with the right machine can't be bothered. I'd probably go with one of the jig systems myself or make my own jig with very careful layout.

[Brad Shipton]

That is interesting Ted. I have never had tapered holes, but I did have some oblong holes long ago when I did not always check my tolerances as carefully. I did a small project a few years back for someone where the a lot of dowels had to fit into holes, but the holes had to be quite reasonable so the dowels would not fall over. I nearly lost my mind, but I learned a lot about my machine. Small circular pockets are not the best on smaller machines. When I crank up the cut speed I can feel my machine vibrate back and forth a little bit and my machine still weighs 2600lb. There is a reason the industrial machines tend to weigh in around the 6,000lb+ mark.

[Jim Becker]

I just watched the video. INCREDIBLE! What an ingenious design! And what a shop! Holy Moly!

Yes, the drilling jig is pure simplicity, although I will admit that the 20mm Freud bit I bought really needs a longer shank...I was, um...just barely getting through the 3/4" MDF with my jig being 1/2" thick. It's also only 1/4" shank and I'd prefer 8mm or 1/2" shank for this kind of job. If I make more tops, I'll likely look for another 20mm bit for the 'drilling'.

As to the rest of Timothy's setup...yea...it's really well thought out and executed. I'm building his MFSC and although there have been a few minor cut list issues, it's going well.

[Jim Becker]

Cutting out these holes on a CNC is not that complicated, but I do agree you need to add a tolerance spec to the diameter callout for circles on your drawing. The tolerance should read 20mm -0.000" / +0.010" (assuming the exact diameter of the MFT dogs is 20mm).

The dogs for 20mm holes are typically 19.95-19.98mm. They can't be exactly 20mm or they'd be unusable. But that backs up your +/- specification. Smaller than 20mm is absolutely no-good. "Slightly" large by a tenth of a mm will likely be ok. CNC tool paths also have to be stepped enough to maintain tolerance at this depth of cut so there's no taper from excess lateral pressure on the cutter.

[John Stankus]

On the Alpharetta Georgia craigslist there is a shop that is making these
Also there is a guy selling cad drawings for multifunction slab mfs (google it) so you can get you local CnC shop.
There are replacement mft tops and lee valley has something though it looks smaller
Dominofix has a jig to make your own

Google is your friend

[Brad Shipton]

Thanks Jim. I had never measured my MFT hold downs, so that is why I assumed the size. Industrial CNC machines drive 3/8" and 1/2" diameter bits at 1000 - 2000ipm in many different woods cutting irregular shapes where you would see taper if you bit deflection were a problem. That is the reason they need 25 - 40hp vacuums for stock hold down. The head cannot accelerate to speeds anywhere near that speed for such small holes, so I highly doubt taper would be an issue with a reasonable machine.

[laura vianello]

Thanks Jim, the table would be used to do cross cutting with the Festool track saw. I always have hard time with perfect 90. I created a jig with pins (instead of dogholes) but it has been hard to drill 90, drill perfectly spaced and aligned. I blamed my measurement tools and my power but there is more into this...So I decided to go for the perfect bench. While I can buy the Festool top, it does not have the dimension I want. I will look into your suggestion but I used the router only once and because I do not have dust collection on it, it is not my first choice. However I have not seen that video so I might change my mind. Thanks a lot for your suggestion

[laura vianello]

Thanks, interesting option.

[laura vianello]

I looked into this, however I read a lot about people struggling with aligned peg boards. It is a great idea but it relays on no so grate material that you need to be sure is perfectly manufactured. I got a little scared on spending time on the right peg board. Quality at the big box store is very poor as far as the measurement tool I buy there
Thanks for your valuable suggestion.

[laura vianello]

Jim, see my message above. Thanks for your help. Interesting that you could use it exactly for squaring table.

[laura vianello]

That is a possibility, I wish the table top was not $140 min. It would be nice to have a 1x1 square jig. Bench dogs are on their way!!! Thanks

[laura vianello]

Good point. I think I will get the Parf system and call the day

[laura vianello]

I looked at it but there was a deadline to order. It is passed. Too long of a lead time at this point. Excellent suggestion. Thanks