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Thread: Gramercy Holdfast Help

  1. #16
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    Aug 2006
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    Mine work fine. After I glued leather on and really mauled them with my angle grinder. To be fair I think my table top is too thick but roughening them with sandpaper won't do the job. I set them with a mighty wack.

  2. #17
    These holdfasts seem to be a hit-or-miss proposition. I never got mine to work, even with leather pads and roughing with sandpaper, and sold them to a friend. He likes them. My bench is 3-1/2" ash. Cast ones from Lie-Nielsen worked better.

  3. #18
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    Quote Originally Posted by Mike Brady View Post
    These holdfasts seem to be a hit-or-miss proposition. I never got mine to work, even with leather pads and roughing with sandpaper, and sold them to a friend. He likes them. My bench is 3-1/2" ash. Cast ones from Lie-Nielsen worked better.
    Mike,

    Is there any chance you measured the shaft size of both sets?

    If so was there a difference?

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  4. #19
    Join Date
    Jan 2009
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    Williamsburg,Va.
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    You guys are doing something wrong. We used holdfasts all the time in Historic Trades,and I never used but one at a time,nor did the cabinet makers next door. We might have had better holdfasts. Mine is quite heavy duty. I need to take a picture of it. From what I've seen,mine is considerably more stout than even the ones Peter Ross makes. It's corner,between the shaft and the arm,is quite solidly filled in. No way can it ever tend to bend under the force of driving it in tightly to hold the work. Yes,it needs to be used with a loose fitting hole,in a good,hard maple or other similarly hardwood top. My bench tops have always been about 4" thick. You need the bench top to be good hard wood in order for the holdfast to bind well.

    Oh,yes,you could intentionally force the wood to go sideways. But,for any planing operations we ever did,the hold fasts were quite secure.

  5. #20
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    It's possibly worth thinking specifically about how holdfasts work. This is just my take, but the key point is likely that it's the working forces acting with the geometry of the holdfast's straight shank and the hole that create the grip, and much less so friction within the hole/between the steel and the wood. I'd be wary of stuff like punch popping the shank, as it seems likely to risk wear to dogholes and to possibly not add that much that would be consistent - although degreasing (getting traces of oil in dogholes has the potential to cause big problems) and sanding as Grammercy suggest can't do any harm. Wear to/enlargement of the dog hole caused that way could sometimes prove helpful (see below), but it might not be even in all directions.

    Take a look at this quickie sketch:

    sketch holdfast 15-7-14.jpg
    My guess is that the relationship between the shank diameter and the dog hole diameter (the clearance) and the thickness of the top is the key - these together determine the angle marked 'A'. When the holdfast is hammered in and bears on the bench top/holds down the work the result is the reaction force marked 'F'. (it's at right angles to the clamped surface) This (because of the layout of the holdfast - the arm projects out to the side) immediately causes the twisting moment/torque marked R about the point marked +. (located on the shank and somewhere between the bench top and bottom surfaces)

    This torque is resisted by contact with the top and bottom edges of the dog hole - but not before the holdfast has tilted out of vertical (relative to the bench top) by this angle 'A'. It's tempting to think that it's friction at these points that retains the holdfast (and no doubt it helps), but there's likely something a bit subtler going on.

    Force 'F' is basically vertical (relative to the bench top), which means that it acts to try to lift the tilted holdfast vertically out of the hole.

    This isn't possible - because the shank of the holdfast is held tilted at angle 'A', and in this crosswise orientation it can't fit up through the dog hole. So the holdfast is held locked down - the projecting straight section of the inclined shank in effect 'hooks' under the bench top. Whacking the back of the holdfast to release it stands it back up into the vertical (the foot must move horizontally by a small amount to achieve this) - freeing the shank to slide in the dog hole. So it releases.

    My guess is that the key to getting holdfasts to grip is to ensure that angle 'A' is correct. i.e. is enough to permit this hooking effect to work. If it's too small a little flexing of the shank may permit it to slide a bit and release completely. The shank needs to be long enough to project past the bottom of the bench too.

    It'd be interesting to test how effectively a holdfast works for differing values of the angle 'A'. There's various ways it can be adjusted. Too tight a dog hole or too thick a bench top may both reduce it below the required minimum. The common fix of counterboring from below to reduce the effective thickness of the bench top will increase it for a given dog hole and shank diameter/clearance. It should increase the vertical holding capacity (max 'clampable' workpiece thickness) too.

    It wouldn't be too hard to make up a test block and to trial the various hole options before modifying a bench top.

    Has anybody ever tried enlarging the dog hole diameter by a hair in the situation where holdfasts are not gripping well? One downside to fixing a problem by increasing the hole diameter this way (as well as not gaining the extra capacity - and even if it restores grip) might be that it could interfere with the function of some of the other 3/4in dia dog-hole mounting products about. (e.g. the various Veritas locking dogs) it'd depend on what tolerance/how large a hole they can handle.

    Another thought on the causes of the problem (in addition to recently thicker bench tops). Lots are boring dog holes now using routers and spiral cutting bits. Wonder is it possible that these (while delivering a nice clean hole) may tend for a nominal 3/4in size to deliver a smaller dog hole diameter than your average drill bit which tends run a bit off centre/to bore a shade oversize?

    ian
    Last edited by ian maybury; 07-15-2014 at 6:32 PM. Reason: clarity

  6. #21
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    Jan 2009
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    In the 60's I used a blue Marples holdfast that Woodcraft Supply sold. It had the tightening screw on the arm,and was made of cast iron. I had a problem with it slipping in the hole it went into. This was cured by filing a bunch of grooves across the back side of the shank. That way,the shank could better bite into the workbench. I never used the cast iron collar that came with it as that would have limited me to 1 location only for the holdfast.

    I might suggest that you file teeth across the back of your holdfast with a thread restoring file,where it touches the wood. This type file isn't very expensive,and can be had at any auto store,or Walmart. You might also find it useful for "Knurling" knobs,though a real checkering file from Brownell's Gunsmithing would be a lot better. I haven't actually used a thread restoring file for this myself,but it is a thought.

    I haven't had to do this with my hand forged holdfast,but you might find it useful.
    Last edited by george wilson; 07-15-2014 at 8:36 AM.

  7. #22
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    Ok. I have some work to do... my first goal to find the right thickness and hole size. but first... the Ivory paint came today....

  8. Whatever happened with this? I have the same problem and I wonder what the potential solution is? did you every determine the solution to your satisfaction?

  9. #24
    Join Date
    Jan 2010
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    Lafayette, Indiana
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    Michael, you say you have the same issue? How thick is your bench top? Have you glue leather pads to the ends of your hold fasts? I glued a soft suede leather to mind, and roughed up the shank with some 100 grit paper. They are working great in a 3 1/4" thick maple top.

  10. #25
    Join Date
    Jun 2014
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    SE Ohio
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    I use mine in pairs. 3 inch southern yellow pine bunch top. I like to plane across the bench top, using a thin board held on the ends by two hf's. They hold just fine by placing the thin board against the hf's.

    when using one hf's they can work loose.

  11. #26
    I had no luck with the Grammercy holdfasts in my bench. A friend ended up with them and they work fine for him. For the record, my bench is 3-1/4" ash. I had sanded the shafts and put leather pads on them. No dice. Lie-Nielsen cast holdfasts replaced those and work great. I feel if you have to hit holdfasts very hard to set them you are just deforming the dog holes.

  12. #27
    I have a pair and they work very well. I sanded them "round and round, not up and down" like their web site says. My bench top is also yellow pine (just dimensioned lumber), about 3 1/4" thick.

  13. #28
    Join Date
    Feb 2004
    Location
    Perth, Australia
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    9,469
    Matthew, it's a bit of a mystery to me why your Gramercy holdfasts are not holding fasting. I drilled two more holes for mine just yesterday, and - as with all the other holes - they worked immediately. Indeed, they hold so tightly that they take some effort to release.

    Gramercy state that the holdfasts are for a bench from 1 3/4" using 3/4" holes. Feedback is that they do not work well with 4" or more benchtops. My benchtop is Oak and and the holes a nominal 3/4" with brace and bit (don't try to use any other method!). These holes work equally well with the Veritas holdfasts. The only modification I have on my Gramercy holdfasts is to glue leather to the heads to prevent damage to the work piece. It is not for gripping. That is unnecessary. One at a time prevents most movement.

    The only held you will get from the above is that they work very well.

    I would look at your bench material and the holes. I suppose that some woods/wood composites may be too slick to grip - one of the reasons that Gramercy have suggested sanding the shaft for extra resistance. Together with a hole that is tight, there will be too little side movement (very little is evidently needed) to add to the resistance needed. Try roughing your holes before you try anything else (coarse sandpaper glued to a dowel, or a gentle use of a hacksaw blade).

    Regards from Perth

    Derek

  14. #29
    I have no deep knowledge on this matter, but I would hypothesize how perpendicular your holes are makes a difference. I have two holes in my 3.75 thick soft maple bench and the holdfast holds well in one (the straight one) and rather poorly in the other one (which I drilled carelessly at some sort of off 90 angle). Mine are not gramercy but LN.

    I don't know if that's the real reason, though; perhaps there are other variables I am not noticing.

    Good luck with yours.

  15. #30
    Join Date
    Feb 2004
    Location
    Perth, Australia
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    they "stick" but they don't hold. even if I hit them in with quite a bit of force I can still swing the board around with ease, I have resorted to using clamps again.
    Matthew, one more thought.

    Reflecting on the above, that sounds like the pad of the holdfast is not seating firmly or evenly on the work piece (alternatively, your bench has many high spots). Do you place a waste block on the work piece before tapping down the holdfast (it should not need more than a light tap)? A piece of leather under the pad would do this and also protect the work piece from the steel pad.

    Regards from Perth

    Derek

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