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Any suggestions on best thickness for workbench top for use with holdfasts

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Forum topic by crank49 posted 05-06-2013 01:51 AM 2428 views 0 times favorited 7 replies Add to Favorites Watch
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crank49

3456 posts in 1658 days


05-06-2013 01:51 AM

Topic tags/keywords: question

I have a bench I built about 3 years ago that is made of 4 layers of 3/4 plywood, topped with 3/8” MDF and 3/16” Masonite. Total thickness is 3 1/2”. The top is banded with 1×4 maple.
I drilled 3/4” holes for holdfasts and used a 1/4” round-over router bit to smooth the tops of the holes so the holdfast would not mess up the masonite top layer. This worked well, looks good.
But my holdfasts won’t hold. I have seen comments that a top can be too thick for holdfasts to work. A suggested fix is to counterbore the holes from the bottom.

Anyone have a suggestion as to how to counterbore an existing 3/4” hole? – I’m thinking maybe with a router.

The next question is how deep of a counterbore would be needed?

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H


7 replies so far

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shipwright

5084 posts in 1485 days


#1 posted 05-06-2013 02:17 AM

I have Gramercy holdfasts in a 4 1/4” bench top and they work great. They slipped at first but a little grab and twist rub with sandpaper (and I mean a little) and they were perfect. I don’t know how I lived without them all these years.
What kind do you have and have you cleaned up the shafts?
My bench is 5 layers of PW with a half inch of Arbutus on top.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

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Brandon

4139 posts in 1638 days


#2 posted 05-06-2013 02:23 AM

Hold fasts all hold at different thicknesses. You can make sample boards with 3/4” holes in them to test different thicknesses to determine the best thickness for your hold fast, then apply that knowledge to your bench.

-- "hold fast to that which is good"

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BigRedKnothead

5297 posts in 669 days


#3 posted 05-06-2013 02:32 AM

I had trouble with the gramercy hold downs on my 4” thick top. I reamed out the bottom of the holes with a stepped bit, and it took care of it. Hope it helps, Red

-- Red -- "That the powerful play goes on, and you may contribute a verse." W. Whitman

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PSF

6 posts in 536 days


#4 posted 05-06-2013 11:42 AM

When I built my bench, I used 2X4s on edge, glued together. Then I laid 1 piece of 3/4” plywood over the top

-- Pete - Chesapeake, VA

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crank49

3456 posts in 1658 days


#5 posted 05-06-2013 03:01 PM

Thanks everyone for the replies.

Paul, I have been wanting to get some Gramercy holdfasts; and I will some day. Like when I get the farm sold and build my new shop in town at the house I’m renovating. Just have a lot on my table right now.

My holdfasts right now are the cast malleable iron ones from Woodcraft. I have not done anything to the shafts. They are pretty rough, with a sand cast texture and a coat of paint. I did smooth grind and sand the foot, the part that presses against the workpiece, because it had a bad parting line offset and made ugly gouges. I will remove the paint and sand these things down and see if that helps.

Knothead, that stepped drill is a good trick. Had never thought of that. I tend to think of those bits in terms of sheet metal, like for conduit openings, etc.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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GrandpaLen

1563 posts in 959 days


#6 posted 05-06-2013 04:39 PM

Michael,

Are your ‘Dog Holes’ just bored into the layers of plywood?

The glue layers of the plywood itself may be preventing the holdfasts from getting any traction on the surface of the holes.

If you cannot get them to grip you may have to bore or mortice larger holes and fill them with a hardwood insert and rebore your ‘Dog Holes’.

...just a thought.

Best Regards. – Grandpa Len

Work Safely and have Fun.

-- Mother Nature should be proud of what you've done with her tree. - Len ...just north of a stone's throw from the oHIo, river that is, in So. Indiana.

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shipwright

5084 posts in 1485 days


#7 posted 05-06-2013 05:01 PM

The glue layers of the plywood itself may be preventing the holdfasts from getting any traction on the surface of the holes.

If you cannot get them to grip you may have to bore or mortice larger holes and fill them with a hardwood insert and rebore your ‘Dog Holes’.

The dog holes in my plywood topped bench (above) are in hardwood inserts. Don’t know if it makes a difference or not.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

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