20mm Bench dogs and 20mm hole sizes??

[Distinterior]

Rather than create a new thread I hoped I could just re-use this one.

I have the opposite problem than the OP in that the holes on my cheap MFT-style top are slightly too large. As a test, I wrapped one pass of electrical tape around my dogs and that makes them a very tight fit (but they do, just about, go in). I can't imagine the eletrical tape lasting long in this situation so am looking for an alternative solution.
Two that I am considering are:
1) use PTFE tape to make them slightly smaller than the eletrical tape
2) I've heard some finishes to the MFT can reduce the hole size. Perhaps I should apply some varnish or a similar finish to take up some of the space? If so any recommended finishes?

Any thoughts or suggestions? Other ideas?

A version of the UJK Parf dogs that Axminster Tools sells have rubber O Rings on them and would very likely take up any minute play you may have.

Here's a link and a description of how they can be adjusted to take up any excess play.....

https://www.axminstertools.com/ujk-expanding-20mm-dogs-30mm-height-pkt-2-108820

 

[webbier]

I did see them but £40 seems a high cost compared to some of the other options. If I had my money again I would have purchased them though.

 

[Distinterior]

I did see them but £40 seems a high cost compared to some of the other options. If I had my money again I would have purchased them though.

I appreciate that they are not cheap but, possibly your only other option would be to have a set of custom dogs turned and I imagine they would likely be more expensive than the option from Axminster.

Incidentally, I purchased my fixed dimension Axminster Parf Dogs before I had a 2400 x 1200 MFT table made, and I gave the Parf Dogs to the CNC guy to ensure a really nice snug fit.

They are, however, rather loose in my Festool made MFT table top, to the point that I dont tend to use it for very accurate cutting with a guide rail.
The larger table is bang on accurate.....

Edit.
Have you tried fixing your dogs from underneath? Fixing them by means of a knob from below may well remove any slackness...?

The items pictured below also really help to keep the rail snug up against the dogs whilst cutting....

 

[LaurenceCarr]

Benchdog also do one with an o ring (quad dogs). Again expensive, but excellent as are all their products that I have tried.

 

[webbier]

I think rather than go with expensive new dogs or risk over tightening the holes by applying varnish or similar I'll try the tape option as a cheaper fix for now and see how durable they are. Thanks all.

 

[TominDales]

Asking for advice. bought a 20mm dog but have 19mm holes in bench.

I've a few 3/4'' (19mm) holes in my bench top and apron, used for holdfasts and dogs (around the face vice and apron, not many about 4 on top and 8 in in the apron). I have home made wood dowle inserts that work as dogs.

Recently bought a pair of adjustable dogs with clamp from Amazon for £21, it has a screw that allows to clamp similar to an end vice. BUT without realising, it was 20mmm diameter ..... should have realised they gone metric! The adjustable dog is really clever, but do I buy another at right size (19mm) and take the hit, or upgrade my bench to 20mm as new stuff is likley to be that size. I cant really send it back to amazon as its my mistake.

Nub of the question is will the holfasts that are 5/8 diameter work in 20mm holes? The holdfasts work by being angled so 5/8 fits a 3/4 inch hole, but would that work at 20mm, has anyone tried this before. thanks

 

[Sideways]

5/8" is 15.875mm
Just shy of 16mm
Enough of a difference that you don't buy 16mm wheels to fit a 5/8" angle grinder. Too sloppy.
I haven't tried but pretty sure I read about holdfasts for 3/4" 19mm holes being too sloppy in 20mm holes. They don't jam quite as well at the bigger angle allowed in the larger hole.
Can you pop in a new row of 20mm holes for the modern dogs ?
Otherwise just send back and swap for 19mm ones. You have the right of return, it will only cost postage.

 

[Cabinetman]

Holdfasts, it’s all relative to the top thickness, a thick top will work better with a sloppy fit, it’s all to do with the holdfast touching opposite sides of the hole top and bottom.
Will it work? Best way to find out is to mimic your bench top with an offcut and try it.
Ian

 

[TominDales]

Thank you Sideways and Cabinetman. I'll drill a 20mm hole in the bench and give it a try. I built the bench in 1975 whilst at school, using 3 inch thick pine with beach edges - traditional city and Guilds crafts approach, very solid and heavy, and have modified it carefully over the years. It originally had two square dogs that clamped to the legs and I've added more since. I'm very cautious about adding too many modern gimmicks as its done me well over the years.

 

[John Hall]

Wrap some fine sandpaper round a piece of dowel and open up the hole until the dog is a tight fit

 

[TominDales]

Wrap some fine sandpaper round a piece of dowel and open up the hole until the dog is a tight fit

 

[TominDales]

Good suggestion. I didn't like the expense of a reamer £20, when I could buy new dog parts for £22.

 

[John Hall]

Good suggestion. I didn't like the expense of a reamer £20, when I could buy new dog parts for £22.

Exactly…keeep it simple