How much play in the mft holes?

[rjwz28]

I got a piece of mdf and drilled out 20 mm holes on a cabinet shop's cnc machine and there's a little play when I insert the clamping elements.  How much play is there in a real MFT?  I'm wondering how much will it affect my usage.  It's hard to say how much but when you insert one of the clamping elements or dogs all the way down the hole, you can shake it back and forth a little.  What are the chances of the holes coming tighter with the humidity as it is high here?  How crazy would it be to wet the holes with water to see if it swelled a little therefor making the holes smaller?

BTW, a friend did it for free, so I don't want to ask them to redo it.  It is dead on straight and square.  I plan on using it with Parf Dogs with my track saw when I don't want to use my table saw.

thanks,
Rob

 

[Claimdude]

Rob,

I had a custom machined MFT top done by a company in Shreveport, LA. It was spot on. The original Qwas dogs had too much play to suit me but the Park dogs, and custom Qwas dogs with powder coating are a very nice suction type fit. Maybe your friend bored then slightly over sized? The water in the hole idea would likely be a disaster. No way to control it for such a small amount of swelling.

Jack 

 

[greg mann]

I wouldn't fret over it. Even .002 will allow quite a bit of wiggle room and that will have virtually no effect on any application. Look at it this way: because your holes are CNC'd they are probably more accurately spaced than what anyone could do with a holey rail and spacers. That alone, for positioning purposes, will more than make up for the extra clearance isues. Also, when you use the dogs they will load up against the hole wall in the same direction. Lastly, remember that .002 clearance means the hole wall is onlly .001 away from contact, so the position of the dog can only be moved from a perfect center-line by .001.

 

[gkaiseril]

Remember that wood and wood based composites can swell and shrink with the weather. Also if the holes are too tight some accessories might not fit all the time or might not come out. The bench dogs have some play and as clamping force is applied they will lock to the hole. If you think the fit is too loose shim the dogs as needed.

 

[mouppe]

Why would you want your clamping elements to be such a tight fit? They're not like the dogs you intend to use for layout purposes.

 

[MrToolJunkie]

I think a little play is OK -- there is probably that much play in the clamping mechanism itself.

Scot

 

[rjwz28]

Thanks everyone for your comments.  Looks like I'm ok.

Merry Christmas!

Rob