20mm holes on replacement MFT top too small.

[punkmft]

I purchased a replacement for my MFT/3 table top about a year ago from a 3rd party vendor. Everything was great until I purchased a square with precision-cut 20mm dogs. It was then that I learned that the 20mm holes are just a hair too small (maybe. 5mm)to use those dogs. I repurposed the old table top so was able to confirm that the dogs fit perfectly (no slop but sill easy to insert/remove). I am wondering if anyone has suggestions for widening the holes in the new table top to 20mm while retaining their squareness with respect to each other. Or am I better off plunking down the cash to replace the table top again?

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[Lincoln]

This happened to me, with a custom top I had CNC'd.
To fix it, I used a 3mm round-over bit on all the holes, on the bottom/back side.
Then, I used a straight bearing cutter from the top/front side and set the depth so that the bearing was running on the rounded over part of the hole. This increased the diameter of the dog holes by the .5mm I needed.
If you need to take more off, drop the bearing cutter a little deeper, so it runs on a more 'rounded over' section of the hole edge.
Worked surprisingly well.

 

[DeformedTree]

I purchased a replacement for my MFT/3 table top about a year ago from a 3rd party vendor. Everything was great until I purchased a square with precision-cut 20mm dogs. It was then that I learned that the 20mm holes are just a hair too small (maybe. 5mm)to use those dogs. I repurposed the old table top so was able to confirm that the dogs fit perfectly (no slop but sill easy to insert/remove). I am wondering if anyone has suggestions for widening the holes in the new table top to 20mm while retaining their squareness with respect to each other. Or am I better off plunking down the cash to replace the table top again?

Have you contacted the vendor that made it?  Did they advertise them as having 20mm holes or did they not explicitly state that?  I'm guessing they have made them 3/4" in an act of just not caring/ignorance/ameri-fication (if you are in the US). Could even be a manufacturing mistake (someone doing conversions along the way grabbing wrong tool).  Far too many things get labeled 3/4" (20mm) which is obviously non-sense but folks/companies do it all the time. Thus why dual dimensioning needs to be banned unless showing the true values of both systems.

I wouldn't go getting a replacement from the 3rd party without clarifying. Far as enlarging you might be able to use one of the kit/fixtures for making them on your own to set up to enlarge them. But that's probably more work than just buying a new one.

 

[Stone Message]

I have had direct experience of the random accuracy errors of CNC work and heard of several others like this. I am sure that the majority of CNC operators will take the time to maintain the accuracy their work but some do not do regular checks of cutter wear and homing.

I would suggest that anyone putting work out for bench tops for dogs holes give the CNC operator one of their bench dogs as a checking tool. Before you pay the guy make sure that your dogs fit.

Alternatively use the Parf Guide System. I am sorry for this blatant advertisement but it is the reason the tool was created.

To overcome the issue of the hole size being too small get a known good 20 mm cutter that you know makes a hole suitable for your dogs. Then carefully enlarge the holes. The final top will not be as accurate as a PGS created top but it may still be good enough for routine work.

Peter

 

[Sheik Maboutie]

I think you have to consider that most MFT tops are made from MDF, if left in a unheated or damp garage or workshop you can expect some movement or swelling which can reduce the dog hole sizes.

 

[punkmft]

Thank you all for your feedback. The vendor - who sells through Etsy and Ebay - does advertise as creating tops with 20mm holes (I went back and checked). I suspect as Peter suggests that the CNC system used is off by a hair (I had a bit of a fanboy swoon when I saw your post lol). I will consider the feedback offered and may very well go with the PGS as the more Parf fence approach has got me thinking about moving away from the Festool fence protractor I've been using. [emoji4]

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[jeffinsgf]

Reaming the holes by hand is a quick, accurate and low-cost solution
https://www.amazon.com/20mm-Straight-Shank-Hand-Reamer/dp/B00OK07K9A

or something like it.