20mm Bench dogs and 20mm hole sizes??

[Phil Pascoe]

Because they don't need a slight taper?

 

[Sideways]

Why don't they make the metal ones with a slight taper?

I guess because anything less than about 7 degrees (isn't it ?) makes a self locking taper and the dogs would have to be knocked out from below. Other than that it's a great idea. No more slop.

 

[bp122]

In one of the videos, Mr. Peter Parfitt said the ujk dogs were 19.98mm, which is what I measured them to be within .01mm of that value.

 

[Jacob]

I guess because anything less than about 7 degrees (isn't it ?) makes a self locking taper and the dogs would have to be knocked out from below. Other than that it's a great idea. No more slop.

They'd just have to be long enough to get at them with a little hammer. Being tapered they could be as long as you like.
But for those who can't get at the underside I'm sure the suppliers of these sorts of things could device yet another gadget to pull them out from the top. Selling gadgets is what it's all about, but I suppose a single design fit-all dog would defeat the object.

 

[Agent_zed]

seem to be plenty of example on google images of bench dogs with sping clips to ensure they stay where you want them. Doesn't look hard to make some or modify existing one.

When I've needed to expand a hole I've just taken a piece of dowel and cut a slit in it and put a peice of sandpaper in it then used that in a drill.

 

[Wattsjoinerybarn]

Could be your top is too thick! Also try chamfering the holes or rounding over with a trim router! Essential for not nipping your finger when sliding stuff over too!

I have pretty much only ever used a 20mm cutter in 18months and 20mm electrical conduit with stop ends or joiners on cut at different heights for different tasks. Somedays you bang them in and out and other days it’s a wiggle.

I do own some bench dogs but can’t see they are worth their money tbh!

 

[Phil Pascoe]

Could be your top is too thick!

It may well be - but it makes no difference if the dogs/holdfasts don't go into the holes.

 

[Jacob]

Thinking about tapered dogs again:
Could be the answer to all above probs, assuming the dog-hole is accurate to start with.
A tapered dog would line up precisely with the non tapered hole, on the side where pressure is applied.
Removal could be easy if it was drilled to take a tapered drift as many morse tapers are.
One size dog would fit accurately into holes within a range of diameters.
If accessible from underneath a long dog could be tapped out easily.
Why are dogs round? Isn't clamping pressure always either along or across the bench? A trad planing stop is always square - which helps keep the workpiece steady.
PS have never felt the need for a a so-called MFT myself and all these doggy probs would put me right off! What next, poo bags? My trad bench is already multifunctional - you'd be surprised at some of the things I've done on it.

 

[Agent_zed]

Thinking about tapered dogs again:
Could be the answer to all above probs, assuming the dog-hole is accurate to start with.
A tapered dog would line up precisely with the non tapered hole, on the side where pressure is applied.
Removal could be easy if it was drilled to take a tapered drift as many morse tapers are.
One size dog would fit accurately into holes within a range of diameters.
If accessible from underneath a long dog could be tapped out easily.
Why are dogs round? Isn't clamping pressure always either along or across the bench? A trad planing stop is always square - which helps keep the workpiece steady.
PS have never felt the need for a a so-called MFT myself and all these doggy probs would put me right off! What next, poo bags? My trad bench is already multifunctional - you'd be surprised at some of the things I've done on it.

aren't bench dogs adjustustable so their height so they can be lower than the workpiece? If you have a tapered dog it would get tight at a set height and that's all you can do. Not really practical on my bench to have tapered as if i had to knock them out from below it would be a proper faff as I've got an english workbench with a 12inch apron down the front.

As for MFT benches, as much as I like my english workbench with leg vice it is rather bulky. So it depends entirely on your circumstances as to whether it is better or worse.

Seems like some over thinking is happening as long as the bench dog goes in the hole and is reasonably tight fitting it'll do the job

 

[Adam W.]

I believe that the MFT system was originally intended for site based workers with a thing about Festool stuff, but has been adopted by shed based workers because of its collapsibility and shinyness.

 

[Jacob]

aren't bench dogs adjustustable so their height so they can be lower than the workpiece? If you have a tapered dog it would get tight at a set height and that's all you can do. ....

Wooden dogs. Trimmed to fit.

 

[Agent_zed]

Wooden dogs. Trimmed to fit.

Not sure what you mean. Do you mean have multiple sets with different heights? a taper will only fit to a set depth, you can't just push it further in regardless of what it's made from.

 

[Jacob]

Not sure what you mean. Do you mean have multiple sets with different heights? a taper will only fit to a set depth, you can't just push it further in regardless of what it's made from.

You could have a collection of tapered wooden dogs and shorten them as necessary to fit the workpiece.
I'd see them as consumables - easy to knock them out on a lathe but could be bodged by other means.

 

[Stevebod]

..if only I had a lathe ....

 

[Phil Pascoe]

Nothing like creating a problem where there isn't one.

 

[Windows]

Two dogs in an MFT top create a line, three dogs create an angle (primarily, but not only, 90 degrees). Relative position of the dogs defines both angles and distances. Dogs are round because the workpiece/track touches different parts of the dog at different angles. A chamfer on a dog can be useful for getting it in to the hole, but it would be harder to ensure that a tapered dog is truly vertical and you’d need to be sure that the workpiece/track is not touching the tapered part or you’d essentially be using different diameter dogs which will throw your angles off. Dogs in an MFT top aren’t just for work holding (like a planing stop would be), they’re for alignment.

 

[Windows]

For those not well versed in dog technology, metal dogs are available with a rubber ring to allow the dog to be tightened up and locked in the hole. The dog consists of an upper and lower part joined by a thread with a rubber/plastic ring in between. When the upper part is screwed closer to the lower part, the rubber ring is compressed between them, squeezing it out sideways so that its diameter increases making tight contact with the hole. Unscrew the parts slightly to decrease the pressure and allow the ring to return to its natural diameter and the dog can be removed from the hole.

 

[webbier]

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?

 

[Sideways]

Anything that makes the mdf swell a little could work. The holes tightened up on me when I waxed the mft tip with briwax or some such that becomes pretty wet at hand temp.
Another type of tape is called kapton. It is used in electronics and is relatively thin and tough compared to electrical tape. Ebay ... and made in many widths.

 

[Chief Sawdust Maker]

I often use a piece of 20mm plastic electrical conduit black or white, cut to length and slight chamfer with some sand paper
These are really useful on my cnc which has a grid of dog holes, it means that if you get a tool path wrong you usually dont break a cutter or carve into an expensive dog

Give it a try