3/4" Bench Dogs - clearances for making your own.

[PlacidCasual]

Hi Guys

I'm looking for some advice. I've asked a colleague to knock me up some bench dogs/stops for my home made workbench. I have a 19mm auger bit like the ones in the link below.

https://www.workshopheaven.com/star-m-j ... ngles.html

Not being a machinist and not having done this before I'm not sure what a comfortable clearance on the dog should be.

I was going to guess 18.8mm +0/-0.2mm giving me a 0.2-0.4mm diametric clearance. How does that sound going into 19mm holes, some in ply others in C24 timber.

Some of the stops will be used to support boards going along the skirt into my vice. So the hole is not vertical but horizontal. The dogs/ stops will all be stainless steel 25mm diameter stepped down to my clearance fit.

Any advice much appreciated.

 

[That would work]

Firstly I think you are way too concerned about the dimensions (a bench dog is not precision clock making) but anyway why not bore a few holes in scrapwood and try it out?

 

[marcros]

3/4" wooden dowels with a ball bearing catch (I forget the correct name for this, but Peter seften sells them I think) inset into them.

 

[PlacidCasual]

Well as an engineer I'd like a smooth clearance and not sloppy. But whilst I would happily state the clearance for a steam turbine, wood is a different beast.

I haven't drilled a hole yet, but I could provide a wooden sample and let the machinist work it out for themselves. It was just timing wise that doesn't work as I'd need to go home grab the bit drill a test piece and go back to work.

Just testing the water to see if anyone had any useful experience.

 

[Distinterior]

When I had my 8' x 4' MFT top made by a guy with a CNC machine, i lent him some dogs to use to ensure they were a snug fit in the holes...They were a perfect snug fit. The holes, if cut to metric sizes are supposed to be 20mm dia, but he thought 20mm may be a bit loose after he measured my Festool & Parf dogs. He CNC'd the holes slightly smaller and 3 years later, they still fit a treat.
They are still a bit loose in my Festool MFT top though, as they were from day one...!

 

[Phil Pascoe]

Mine work perfectly in a 60mm hardwood top. The steel is 18mm and the holes are 19mm.

 

[PlacidCasual]

That's helpful Phil. My guess might be a bit tight, I might aim for more 0.4-0.8mm clearance then.

 

[Phil Pascoe]

Too little clearance and they wouldn't jam properly.

 

[Trainee neophyte]

[youtube]qt0QkXxogRE[/youtube]

@3:30 he explains how they work, and suggests you need 3mm clearance.

I haven't made any, so can't comment - hope it helps.

 

[galleywood]

Do they need to be metal?
You could adapt Paul Sellers design, which has a bent wire spring to keep the dogs in place.
https://paulsellers.com/2013/03/poor-ma ... odworkers/

 

[AndyT]

Save the advice about holdfasts for later.
As for the dogs, make them out of wood.
Adjust the size until they fit as required. They don't need to be tight as any slack will be taken up by horizontal clamping or the weight of a board on edge.

You can thank me when you hit one with a plane, chisel or saw and don't ruin the tool.

 

[MusicMan]

Holdfasts do need clearance to jam, dogs don't and can be a smoother fit. Some dogs have thin metal or even wood springs to hold them in place. Don't overthink the clearance! Just get them in so they don't rattle (speaking as another ex-precision-engineer).

 

[Sideways]

0.1mm to 0.15mm clearance is enough / best.
I have a cnc'd MFT clone that was supplied with some perfectly fitting alloy dogs.
Later I bought some veritas dogs to expand the collection. Their fit was in the 0.2 to 0.4mm range you propose and they were far too sloppy.
I returned them and axminster accepted without quibble.

 

[Steve Maskery]

Talking of keeping them in place, my dogs all have a wooden spring. Great when they were new, but after 20 years of being under pressure, there are all bent and work less well. Some have actually broken.
I'm incline to make my next batch just a loose fit, stopped by a crosspin. A couple of different heights would be all that was needed.
S

 

[MikeG.]

Well as an engineer........

Just testing the water to see if anyone had any useful experience.

Wouldn't the engineering approach be to make a mock-up/ master, learn your lessons from that, then put that into practice for the production run?

Right, so make a wooden mock up, adjust as necessary, measure the result, and pass it on to your machinist.

 

[MusicMan]

Though we also believe in not reinventing the wheel!