Case to standardise round bench dog holes at 20mm rather than 3/4in?

[ian maybury]

This unashamedly triggered by James N's current thread on hole size options relating to the Festool MFT system, and some of the posts there. (thanks James) Also by the recognition that there's a huge listing of Festool and Festool inspired/compatible work holding accessories starting to come available. e.g. QWAS and some budget versions of the Festool and Workmate stuff that i hadn't seen until now.

There are probably many more (??), but I'm aware of at least three groups of workholding equipment that may be used in a bench: traditional 3/4in round holdfasts and dowel based dogs, the pretty comprehensive Lee Valley line of 3/4in based working holding accessories (Bench Dog/Pups/etc), and the above 20mm based Festool/Europen inspired hardware which seems to be fast gaining ground.

Thinking about the scenario it seems like it would make a lot of sense if there was some sort of standard. 20mm may offer some benefit even for bench dogs and holdfasts anyway. It'd avoid our being forced to choose between systems, and would for example enable stuff like a traditonal workbench set up to utilise all of the above groups of workholding hardware. Maybe also some of the layout and modularisation thinking in the Festool MFT system - not sure as i'm not familiar enough with it. How's about it Lee valley?

The other factor is the problem that many seem now to be experiencing in getting standard round holdfasts to grip in a 3/4 in hole in the now pretty commonly much thicker than 2 - 2 1/2in thick bench tops - especially when drilling the holes using a router cutter which delivers a hole close to an actual 3/4in dia (19.05mm) unlike the typical spade drill or whatever. I've posted at length about this before without anybody picking up on it - but i'm pretty sure that the problem is that the shank of the holdfast needs to tilt over by a minimum angle for it to lock - for the projecting straight end of the shank to hook under the bottom surface of the bench top. The implication of this is that for a given (say actual 3/4in) shank diameter to grip the dog hole diameter (or the clearance between the two) must be increased compared to what works fine in e.g. a 2in top. It's counter intuitive, but seems likely that the fit needs to be looser for the holdfast to grip tighter.

Might your typical e.g. Grammercy 3/4in holdfast in fact work very nicely in a 20mm dia bench top hole? Has anybody tried it? (even accidentally?) 20mm would meanwhile add a bit of desirable extra robustness to round bench dogs.

If the hodfasts proved to work well at 20mm dia then the Veritas group of workholding products are the obvious stand outs designed for 3/4in holes, although there are no doubt more about. It may be less of an issue than it seems - Lee Valley makes no great effort to specify the actual hole size range (tolerance) their hardware works best in. They just nonchalantly advise a 3/4 in hole. Yet lots of the hardware incorporates expansion devices of once sort or another - which looks very like they might (??) at least in some cases handle the probably less than 0.5mm extra dia to 20mm. (above the holes being bored by some nominally 3/4in drills already e.g. power augers and the like)

I'm going to run some trials once i get a few other jobs out of the way, but it'd be dead interesting to hear some views or better still of experience in this territory..

ian

[ian maybury]

Just trying once more. Has anybody tried 3/4in holdfasts in a 20mm hole in a thick bench top?

[Chris Padilla]

I actually haven't but since I have 2 MFT1080 along with QWAS stuff and the Veritas Dogs/Pups, I can give 'er a go and report back. I bought the Veritas stuff a long time ago when I had planned to build a traditional bench with 3/4" dog holes. I guess I still plan to do that but so far, it is still in the design phase.

[ian maybury]

Thanks Chris. Don't go to a lot of trouble - I'll definitely be running some trials in a while anyway. I'd mail you a Grammercy holdfast to try, but i'm the wrong side of the Atlantic. It'd be useful though to get some advance input, even on the Veritas stuff...

As above the thought has been in my mind for quite a while and James' thread suggested putting the topic up.

I'm another with a trad bench just about to start ( it's finally getting there - but i thought so back in the Autumn too), so i've an ulterior motive.

[ian maybury]

I've just noticed that Veritas/Lee Valley actually now to do many of their workholding solutions in 20mm dia form - several '20mm system' items are linked from this web page from Dieter Schmid Tools in Germany: http://www.fine-tools.com/werkstatt.html

It's possible that they are produced specifically for use in Europe, but they do seem to exist.

If as seems likely (but subject to testing as above) it turns out that an e.g. Grammercy 3/4in holdfast works well (better?) in bench tops over say 2 1/2in then the way may well be open to set up a traditional bench with exclusively 20mm dog holes...

[Rod Sheridan]

Ian, most of the world is metric, why wouldn't you use the 20mm holes if you have accessories in your area that fit thaem?

Regards, Rod.

[ian maybury]

Hi Rod. That's where i'm headed. The only constraint for me since my longstanding bench project is just about to start is that I have a set of 3/4in Grammercy holdfasts, and plan a bench top something over 4in thick. Which seems likely to require the larger dog hole diameter i've posted about before anyway to get them to grip as intended. A few tests will sort out how well they work in 20mm holes in short order.

My reason for posting was mostly just to air the thought that it seems likely that we're likely headed for 20mm dia as the standard for dog holes given the increasing amount of manufactured work holding equipment as above that's made to fit this size anyway - that it perhaps makes sense for anybody building a bench to consider this as a means of making possible a single size dog hole that will accept pretty much everything that's available.

I thought it might be nice to as well (since at this stage there may be some hidden disadvantages) to hear if anybody else had views on the matter (i've seen people bitch elsewhere about having to use mixed size dog holes), and given the holdfast grip issue if in fact anybody had gone so far as to try a 20mm hole with a 3/4in holdfast, or with any of the 3/4 in Veritas hardware yet.

ian

[Chris Padilla]

I STILL need to go try out the MFT w/Vertias pups/dogs. I will do it and post. I was all ready last night after finishing my evening chores and then the daughter wanted to watch Star Trek: Voyager and so it got shelved to Friday. I'll even snap a few pics to make it more exciting.

[Nathan Birrell]

Lee Valley's page for the Gramercy Holdfast states it will work in a 3/4" or 20 mm hole.

Been toying with the idea of making a hand-tool bench that doubles for my Festool with 20 mm holes and using my Veritas Surface Vise and Hold Down. I mean, 3/4" is 19.05 mm, so I don't think that it should be a problem for most of these tools with how they work. I am sure some of my 3/4" holes in my current bench are clsoer to 20 mm now anyway.

-Nate

[Peter Stahl]

I'm just mostly a virtual woodworker anymore but if I were doing a bench I would do the 20 mm holes. 20 mm holes are 0.7874", that's only 0.0374" bigger than a 3/4" hole.

[Lee Reep]

I'm not so sure you'll see the 3/4" size bench dogs and accessories vanish anytime soon. I built my own super-sized MFT-style workbench, and went with 20mm holes since I had purchased Qwas Dogs to use with my Festool track saw. I now also own Parf Dogs. I have some older Jorgensen clamps that have 3/4" posts, and they work fine in 20mm holes, since a precision fit is not required, and the quick nut is large enough to adequately keep it anchored in the 20mm hole. I broke with Festool tradition and went with 4" hole spacing, rather than the MFT spacing of 96mm. There is nothing magical about that spacing -- it could have been 100mm. I CNC'd my benchtop to 36X84 (basically I wanted a foot off each dimension of the MDF sheet to better fit in my shop). This size dictated using 4" to evenly spread them in each direction, with 4" spacing chosen since it is reasonably close to Festool's 96mm anyway.

Now, what bugs me more than bench hole size non-standardization is the insane number of connection sizes for shop vacs. I have a box full of adapters, and none really seem to adapt Brand X shop vac to Brand Y hose to Brand Z tool. And if it was not bad enough that we cannot figure out in the Imperial world, we have metric hoses too.

Let's demand standardization on this first! (And let metric win -- I want to add a Festool dust extractor to my inventory and send the shop vacs packing ...)

Final Note: I bought a Bosch VAC-005 hose for my track saw. It fits my Ridgid shop vac, and has the Festool-style (Euro standard?) connector on the other end, and fits the track saw perfectly.

[ian maybury]

Probably not (disappear that is) Lee!

I'd missed that Lee Valley had the Gramercy holdfasts, and that they recommended a 20mm hole in an 1 3/4 to 2in thick bench top as being OK. Grammercy actually say 3/4in in the same thickness range. That at least gives the information some credibility. My advice is still to make sure to drill some test holes in scrap before tackling a new bench top though.

People keep on running into trouble getting these holdfasts to grip in thick bench tops, and the discussion keeps on heading down the road of roughening them up and the like. Which no doubt helps, but probably needs a larger do hole for a full fix. I've posted a few times on how they likely grip primarily by using the tilt angle when locked down (combination of hole size and bench top thickness) to hook under the bench top.

To run some numbers based on tilt angles. A 20mm dia hole in a 2in (50.8mm) top means the shank can tilt by .95mm in 50.8mm = 1 deg, 1.2 deg in the case of an 1 3/4 (44.45mm) top - both OK according to the makers. Based on the their numbers the minimum tilt they likely grip well at is probably about a brad point drilled hole (say 19.25mm dia) in a 2in top = 0.35 deg.

So whether intentionally or not the makers seem to be suggesting a tilt angle of between 0.35 and 1.2 deg as working best with these 3/4in (probably a thou or so under nominal size) holdfasts.

This has significant implications if you double the top to say 4in (101.6mm) thickness, and still use a brad point drill giving ahole of 19.25mm dia. It halves the tilt to a hair over 0.1 deg - around 1/3 of the minimum required.

The numbers are easily handled. If we take a good robust minimum tilt as our brad point in an 1 3/4in top, the tilt is 0.25/44.4mm. It's simple proportions - if the bench top is doubled in thickness to 2 x 1 3/4 = 3 1/2in (typical of many these days) then maintaining the same tilt requires a hole of minimum dia 2 x 0.25mm = 0.5mm larger = 19.5mm. Probably better if it's larger still, likely the 20mm discussed. From the maker's' numbers it seem likely that up to 21mm dia might well be OK once over 4in (100mm) thickness.

Think I'd be counterboring the dog holes from underneath to effectively reduce the thickness of the top to maybe 3in though - to maximise the holding capacity. It's a pity Gramercy don't offer them with a longer shank as an option..

All that's needed now is some testing to verify this lot...


+1 on standardisation of vacuum fittings and accessories. I've recently had to buy a replacement hose connector for my Bosch GAS 25, and was shocked at the price for a simple plastic fitting that should costs a few €...

[Jim Dwight]

I'd like to standardize on fractional inches, not metric. I don't think in metric and I don't think I ever will. Every time I see a metric dimension I have to convert it before I have a feel for what it is.

I also have had fun with shop vacuum connections. I put a dust deputy on my old 6 gallon Rigid shop vacuum and recently built my version of the Woodsmith cart for this combination. I hooked the cyclone to the shop vacuum with 2 inch plumbing pipe and connectors. I had to heat it a little to get the pipe to conform to the cyclone's outlet. I did the same thing to get connectors for my table saw and CMS and to connect my Rigid hoses to the Cyclone. 2 inch PVC is pretty cheap. I actually used 1 1/2 inch on the CMS. I also used "real" duct tape - aluminum tape about 2 inches wide with an adhesive backing - to make small adjustments in diameter to get things to work. Long way of saying you can make your own fittings out of plumbing pipe an aluminum tape.

I also like that Bosch vacuum hose (VAC-005). I read it's a clone of the Festool hose at a much lower price. What I know for sure is the big end hooks to my cyclone inlet well and the other end connects to my DeWalt track saw just fine. With adapters, the small end also hooks to my Hitachi CMS and my old Ryobi RAS.