Hold-down "Combs" for Non-magnetic Material --- Construction Details
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    Default Hold-down "Combs" for Non-magnetic Material --- Construction Details

    First, I have spent an hour searching old threads trying to find the information on my own as I know this has come up several times. I did find reference to the combs, notably by smt, but I could not find close-ups to see exactly how they are made. Nor did I find a current or prior manufacturer.

    Could some kind soul post a couple of clear close-ups of their combs with a few dimensions and any pointers on possible improvements? I need to make some miniature combs and would like to benefit from prior "art." I did find a few pics on a Blade Forum that indicates there is a thin long metal hinge along the length of the fingers near the mid point that allows the "base" portion to remain flat while the finger portion flexes upward. That hinge appears to be flat in section and I thought it might be better if it were shallowly biconcave as it would have less tendency to crack due to repeat flexing? Grinding that thin hinge without burning the metal might be interesting. Alloy selection might or might not be important?

    And knowing who makes or made them could assist in finding them on auction sites as I will want to buy some full-size ones. (I hear they are not cheap)

    Thanks in advance.

    Denis

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    I found a couple different pics that are nearly identical, so apparently someone used(?) to manufacture these. No luck finding a source however. Why not just take a shot at making your own?
    I've used them before and they were in a plastic case, but that was so long ago I have no idea if they had a name on them or not...

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    Hermann Schmidt sells them

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    Just saw a set at a local auction and they went for a high price. I will search my notes and find more information if I can.
    Could not find the auction but think they were Magna Lock Grips.. and think they went for around $200.. too high as I bid perhaps $40 if even that.

    Here is an old (sold) set on Ebay.
    Magna Lock Magna-Lock Grips hold downs tool machinist toolmaker USA | eBay

    I think it a good idea to grind a 5* to 10* angle off the edge on the narrow side so setting on the chuck the very top point is touching the part..Yes that makes them right and left only with setting them on the wrong side dangerous.

    Making a set would be easy with having a parting wheel on a surface grinder or a slitting saw on a mill, Think I would make the comb all go the same way.
    Think I would make them perhaps 48 on the low side, 60s and mid 60s on the hard. 60s might be best

    Perhaps just start with a set of thin parallels and part them up.
    6 Inch Long x 1-1/2 Inch High x 1/8 Inch 682864 - MSC

    Have had good luck with making thin flat parallels that were only .005 or .010 below the part height to be held with a 5 or 10* angle away from the part top edge. Yes then only one part size spicifice. .

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    Buck,

    For the cost of materials, your idea of cutting up parallels seems like a great idea. There is no way I could buy tool steel for a pair of combs even close to the price of an import SET of parallels. I appreciate the angled cutting edge detail. Sounds spot-on. Maybe I willl forget about the hinge shown in the Magna-Lock set. I can see where it could have some value though...

    Denis

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    A2 for about $18 and change for 18” puts 1/8 x 1 ¼” at about $6.12 each for a 6" spring parallel. Add heat treat and grinding perhaps $12/$15 each. 1/4 x 1 1/4 about $9.72 each just for stock.. *Agree to buy Mfg’s store brand for about $35....
    I once bought a roll of special double back grinding tape for perhaps $60 and it was no better than carpet tape for about $4 bucks.
    Big trick is to take stock on the grind side not the climb side for chancy parts.
    Set part a perhaps 10* angle to long travel so part wants to tighten to the block-in side, with also having a solid go-end but.
    I have held down with Elmer's glue and even one job with whole milk under the part. Also ground a wood part with whole milk as the anchor..

    The hinge? If they came out of flat one could make the out of flat side concave down so having a draw down effect.. that is interesting.
    Last edited by michiganbuck; 12-02-2016 at 07:02 AM.

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    Look at google images for "perma clamp" and "magna grip". I wasn't able to find a current manufacturer so maybe the sets that are out there just keep changing hands.

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    This is a pair of MagnaLock hold downs, Big Rapids, Michigan. Patent Number 2477297.
    Looking at the pair with one face up the other face down.
    Set the pair to the part face up as the finger side is canted up.
    magnalock-.jpgfingers-angled-up.jpg
    John

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    Quote Originally Posted by jhruska View Post
    This is a pair of MagnaLock hold downs, Big Rapids, Michigan. Patent Number 2477297.
    Looking at the pair with one face up the other face down.
    Set the pair to the part face up as the finger side is canted up.
    magnalock-.jpgfingers-angled-up.jpg
    John

    Interesting! I did not realize they had the partial fold in the faces as shown. How do you think that affects their performance vs how they would behave if they did not have the hinge and fold?

    Thank you for that profile shot.

    Denis

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    Quote Originally Posted by dgfoster View Post
    Interesting! I did not realize they had the partial fold in the faces as shown. How do you think that affects their performance vs how they would behave if they did not have the hinge and fold?

    Thank you for that profile shot.

    Denis
    Hey Denis,
    Dimensions using calipers.
    Length 6.365" and 6.367"
    Width ~1.618"
    Height 0.066"
    Slot Depth approximately 0.015 and 0.035 per side leaving 0.011" to 0.010" as the the slot cross section.
    Angle of inclination approximately 3.5 to 4 degrees.
    Face of the fingers has to be ground parallel to the back face. Picture an end view to image the left and right (finger) faces.
    0.750" Distance from back face to edge of slot.
    0.130" to 0.134" Width of slot.

    "how they would behave if they did not have the hinge and fold?"
    The hinge action is critical. The surfaces parallel to the magnet become a fixed point. The two inclined surfaces have enough freedom of motion to hinge downward to the face of the magnet. This motion results in two force components. One downward and one horizontal. The two horizontal forces hold the part while the downward forces pin the part to the face of the magnet. This is where the grind on the face of the fingers is important.
    In some cases it is good practice to place backups parallel and butted up the the back edge of the hold downs. Without the backup the hold downs may scoot away from the part as the hinge surface is pulled down.

    "if they did not have the hinge and fold?"
    The hold downs would lay flat on the magnet and have very little effect.
    An alternate tool is the Starrett tool #54 solid hold down used with an accurate vice. I have some scaled up versions that are about twelve inches long. Purchase air or oil hardening stock at finished width and then grind the angles and reliefs.
    Regards, John
    Last edited by jhruska; 12-02-2016 at 07:55 AM. Reason: tech note

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    A little off topic, but had I known these were apparently so rare, I would have scooped up some back when I did more toolmaker type work...

    Reminds me of the 1c collet set I had, bought it for $20, sold it for about the same, now I want them again and see some individual collets are $100+ !! I had something like 10-12 collets, 2 of the 5/8" round holders, and the lathe block thingy <sigh> oh well I guess.

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    Quote Originally Posted by jhruska View Post
    This is a pair of MagnaLock hold downs, Big Rapids, Michigan. Patent Number 2477297.
    Looking at the pair with one face up the other face down.
    Set the pair to the part face up as the finger side is canted up.
    magnalock-.jpgfingers-angled-up.jpg
    John
    Good that you found the patent Jhruska
    Patent US2477297 - Clamping device - Google Patents

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    Amazon set 1/8... ½" to 1 5/8" x 6” whole set $35... Make a couple hold down sets and save the rest for parallels.

    Machinist's Thin Parallel Bar Set - 1 Pair 1/8" X 6" - Bar Clamps - Amazon.com

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    Well, with all the good information posted above, all the "secrets" of this 1949 invention are pretty well laid out both with respect to the form and use of these interesting holding devices including the reason for the large center hole on the Magna Lock devices. It appears the Hermann-Schmidt clamps simplified the design slightly by only grinding the hinge from one side, but otherwise use the same general plan outline.

    Hopefully, in the next few days I will get started making up some devices using parts of both designs. At a shop where I "work" occasionally they have to grind some 300 series stainless Charpy test sections that are supplied to them as very rough bandsaw-cut weld sections. Holding them to grind to specified size and shape after initial machining has been challenging. I think using some version of this clamping device may make that process easier.

    I am very grateful to all that contributed, especially John and Buck. I also hope this thread will be a good reference for others similarly interested in designing and using magnetic work-holding devices.

    Denis.

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    Quote Originally Posted by michiganbuck View Post
    Amazon set ½" to 1 5/8" x 6” whole set $35... Make a couple hold down sets and save the rest for parallels.

    Machinist's Thin Parallel Bar Set - 1 Pair 1/8" X 6" - Bar Clamps - Amazon.com
    Yup, exactly what I plan to do, full length clamps plus a number of much shorter ones for small or irregular parts. Once setup to grind the hinge, I might as well go for it.

    Denis

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    Perhaps grind the radius and the rectangle recess with the web thickness estimated.. then mag down test to see you get some draw down, then cut deeper if you think that is needed… Perhaps the space off the mag is important so you may have to play with that also..Think about a .030 rad in the corner of the rectangle recess might be better than tight corner.
    Yes use some kind of device or spacer so you don’t mag your indicator.
    Post or send me a private message to report your findings.
    I used them at the big shop but don't have my own a set.
    Buck

    PS I will make a set in the spring.. just to busy now with fishing coming up..and I don't heat the shop full time.

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    Sorry, late to the party! I thought this post was just a show-n-tell, and ignored it.

    Mine (that you mention) are Magna-Locks, though they may have been sold by Ralmikes.

    The hinge is a separate spring steel insert, spot welded in. No suggestion that they have to be made that way. I remember seeing them first in Kibbe, Neal & White text and the description of how they work, so I bought a set as soon as i saw one, before i even owned a surface grinder, lol!

    As you have deduced, the hinge is critical to the optimun performance. The edge bites into the work slightly, and is pulled down, latching the work to the chuck when the chuck is turned on.

    I have used a pair of plain thin parallels, and sometimes a sheet of spring steel, to bite relatively straight sided work. Place one parallel flat on the magnet and the other slightly raised against the part edge. Then switch the magnet on. Then carefully place one against the end of the part ("block the end")to keep it from scooting lengthwise from wheel forces. Of course since there needs to be a set up on at least both sides of the part, using thin parallels and spring steel with backers gets awkward. Also, there is a critical angle where the aslant parallel will bite, vs be too high, vs just lay down flat and actually release pressure when the mag is actuated.

    Perhaps a small set of purpose made parallels with a bevel edge as Michigan describes? I also have a set of Starrett hold down parallels for vise work. Have never tried them on the surface grinder, but it occurs to me that with a rail or loose wide parallel as back-up, they might work, too. I'll measure the hinge thickness in a bit. Seems to be the only thing you might be missing now?

    Is this the post you were referring to?
    For scale, part is about 18" long. You can see I used a lot of other parallels for blocking.





    smt

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    Quote Originally Posted by stephen thomas View Post
    Sorry, late to the party! I thought this post was just a show-n-tell, and ignored it.

    Mine (that you mention) are Magna-Locks, though they may have been sold by Ralmikes.

    The hinge is a separate spring steel insert, spot welded in. No suggestion that they have to be made that way. I remember seeing them first in Kibbe, Neal & White text and the description of how they work, so I bought a set as soon as i saw one, before i even owned a surface grinder, lol!

    As you have deduced, the hinge is critical to the optimun performance. The edge bites into the work slightly, and is pulled down, latching the work to the chuck when the chuck is turned on.

    I have used a pair of plain thin parallels, and sometimes a sheet of spring steel, to bite relatively straight sided work. Place one parallel flat on the magnet and the other slightly raised against the part edge. Then switch the magnet on. Then carefully place one against the end of the part ("block the end")to keep it from scooting lengthwise from wheel forces. Of course since there needs to be a set up on at least both sides of the part, using thin parallels and spring steel with backers gets awkward. Also, there is a critical angle where the aslant parallel will bite, vs be too high, vs just lay down flat and actually release pressure when the mag is actuated.

    Perhaps a small set of purpose made parallels with a bevel edge as Michigan describes? I also have a set of Starrett hold down parallels for vise work. Have never tried them on the surface grinder, but it occurs to me that with a rail or loose wide parallel as back-up, they might work, too. I'll measure the hinge thickness in a bit. Seems to be the only thing you might be missing now?

    Is this the post you were referring to?
    For scale, part is about 18" long. You can see I used a lot of other parallels for blocking.



    smt
    Yes, I was referring to that post.

    The part you noted about the hinge being a separate piece makes sense. I figure if I try to grind the hinge in, that heating of that thin section will be a problem that I hope to mitigate with flood coolant. But then that still leaves the problem of putting the 4 or 5 degree bend or Fold in the spring to get the teeth to angle upward in the relaxed state. I think I will first try grinding in the spring and making the thinned wheel have a slight crown so the hinge is biconcave in cross section. I hope/figure that will reduce the cracking tendency of the spring. I suppose this is what they mean by trial and ERROR. Won't be surprised if it turns out that spot welding the spring into a groove is needed.... Anyone got any better ideas?

    Thanks, Stephen.

    Denis

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    This set is 10" long. Spring is .010 thick. As can sort of be seen in 2nd photo, 4 spot welds along length. The "business" (working/cutting) edges are beveled as Michigan described.





    smt

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    FWIW, the welds had me puzzled so I looked under microscope. They do indeed seem to be welds, mostly kind of cold looking, but there are undercuts where the arc (or whatever?) impinged outside the intended weld area, and also along either the large pieces, or the spring. Lots of cold shuts.

    Not all the "welds" penetrate both sides, but there does not seem to be a pattern. More a "that's good enough to hold it all together" approach. Clearly the close fitting and relatively deep 5/32"+/3/16"-) mechanical connection provides most of the operating characteristics.

    That said, I bet a 1/8" groove & a few tacks of silver solder would work as well or better so long as it did not blob and provide a point of stiff resistance to flex.

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