Hold-down "Combs" for Non-magnetic Material --- Construction Details - Page 2
Close
Login to Your Account
Page 2 of 2 FirstFirst 12
Results 21 to 37 of 37
  1. #21
    Join Date
    Jun 2004
    Country
    UNITED STATES
    State/Province
    Idaho
    Posts
    256
    Post Thanks / Like
    Likes (Given)
    160
    Likes (Received)
    50

    Default

    We use these type of magnetic hold down clamps a lot. Here are a few photos. These just have a groove ground through to a thin section to form the hinge. I don't remember where we got them, they are at least 30 years old. These are photos of 1/16" thick and 1/8" thick, we also have a few different widths. They are marked Metric Systems. Billhold-down1.jpghold-down2.jpghold-down3.jpg

  2. #22
    Join Date
    Aug 2008
    Location
    Sussex, England
    Posts
    3,138
    Post Thanks / Like
    Likes (Given)
    12
    Likes (Received)
    635

    Default

    Quote Originally Posted by stephen thomas View Post
    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.
    Wonder if any of the thin "wicking" cyanoacrylate glues would penetrate the gap sufficiently to give enough bond?

    Way back in the early 1980's I ended up with some special purpose opto-mechanical lab kit using very similar welded on shim steel flexure type hinges mostly made in house. Result looked very spot-weldish but had to go out to a specialist as normal spot welding fried the shim before getting adhesion. I want to think it was a short arc or cold arc process but this long after I can't recall how it was done.

    Clive

  3. #23
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    8,809
    Post Thanks / Like
    Likes (Given)
    2608
    Likes (Received)
    2989

    Default

    The tip up angle off the chuck of the hold down feature (comb) is necessary so the mag hold down forces the teeth ends to push against the work with the arc of the swing so actually increasing the width of the hold down parallel. The .010 shim stock design a very good idea because that would (may) be more durable than simply a thin (,010) section of common part material. It also seems the ones I used were not having the spring insert but a solid design.
    With the comb feature simply being horizontal the mag-down would tend to not expand the width and so would not increasing holding, but would decrease holding.

    Back to the shim or not.. the shim design (Stephen post #19)seems more durable for flexing and long life but the all one piece (BillDe p-#21) easier to manufacture with being one piece not three.
    The set I intend to make will be the bought Parallels and the altered so one piece design.

    With having higher Parallels with the comb angled down but still off chuck they might be knock in Tighteners for a taller part or a low part, but wild depend on the knock-in as the force holding the comb tight. So would work but would be in a different category. The comb hold down would seem best for materials that might be penetrated so being softer that the comb end points. Having angle-up on knock-ins would tend to lift the part up off chuck.

    The Amazon set seems an impossible price because I can’t buy the stock for that price... and a box?
    What material would you think you think these likely import parallels might be? ...and would you think hard through or case hard?
    I will try a rectangle recess on top and radius on bottom.. then two rectangular recesses(Top and bottom) to see what might be more durable .

  4. #24
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Buck,

    i have been thinking some about how to make one-piece combs with a ground-in hinge AND having the tooth portion angle upwards about 4 degrees. One strategy that avoids uncertainty of just bending the hinge (while not breaking it) and having it take the desired set might be to simply, after grinding the hinge, grind off a wedge of material from the sole of the finger side or the base side or maybe even half from both.

    Since the sine of 4 degrees is .069 and the width of the finger side and of the base side might only be
    .625 or so each, if you just ground off a wedge about 20 thou begining at the outside edges of each and tapering to zero at the hinge, you would have a resulting angle of four degrees approximately. Obviously you could also just take about .040 off one side---either the base or the fingers.

    Since you will have cut many many slots on the finger side, it will be lighter than the base and so the base will tend to tip down flat with the mag off---a convenience.

    If the combs were a rarely used item, a person might get by making a bare-bones setup in two separate parts for each side. It would be fiddly, but would work I think to just skip cutting in fingers and just cut the bite angle on the narrow face of say a 5/8" parallels. Then roll up a tiny balls of aluminum foil ( or a bit of rubber band, soft thin packing foam etc) and put one near the part on each side. Now butt the 5/8 parallels against the part and supported near the part by the foil ball. Then block in these parallels with another parallel on each side. Apply the mag, so the down-force and and wedging action occurs. Might be something to do for that rare one-off situation.

    Denis

  5. #25
    Join Date
    Jul 2009
    Location
    Munster, In. USA
    Posts
    2,086
    Post Thanks / Like
    Likes (Given)
    376
    Likes (Received)
    581

    Default

    Three parts each? Wide base slotted, Comb slotted, shim stock to suit, and Loctite.
    John

  6. #26
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Quote Originally Posted by jhruska View Post
    Three parts each? Wide base slotted, Comb slotted, shim stock to suit, and Loctite.
    John
    Sure seems like that should work. Though commercially manufactured ones would be made from 60Rc hardened stock, betcha you could make them from prehard and likely have excellent results. Loctite should work well since the shim is in compression. You could probably just " spot-pinch" the shim in place as well using a punch and hammer to deform the walls of the slot in half a dozen places. Gotta get something made this weekend to try on Monday. Gonna start simple and refine as indicated by need in use.

    Denis

  7. #27
    Join Date
    Apr 2013
    Location
    Damascus, MD
    Posts
    1,156
    Post Thanks / Like
    Likes (Given)
    3295
    Likes (Received)
    644

    Default

    Naive question: why would you want them hardened, beside for withstanding wear? I'd think that relatively soft low-carbon iron would provide more grip to the part, being indeed more deformable, but not entirely soft to deform so much to leave the part free.
    Most of the popular "cold roll" low carbon steels are rather flexible.

    Paolo

  8. #28
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Quote Originally Posted by Paolo_MD View Post
    Naive question: why would you want them hardened, beside for withstanding wear? I'd think that relatively soft low-carbon iron would provide more grip to the part, being indeed more deformable, but not entirely soft to deform so much to leave the part free.
    Most of the popular "cold roll" low carbon steels are rather flexible.

    Paolo
    Very reasonable question. I was figuring the hardened steels would be desirable from a durability standpoint---fewer dings. And I am wondering about the flexible connection. Being unhardened, it will have a low yield strength. Will it crack easily? I am currently in the process of making a 4" long set from 1018. My idea was to just quickly make a small set from 1018 and just see how they work out.

    Attached is a pic of where I am. The hinge needs to be cut, I think the fingers should be cut deeper for more flexibility. I decided to try grinding the 3.5 degree angle into the base as shown. I plan to rough out the hinge on the mill and then grind to thickness using a stone profiled with radii on each side and a flattish center comprising 3/4ths of the width of the hinge. The remaining width of the hinge will be the radii.img_0856.jpg

    I will not be too surprised if this trial run results in a comb that needs tweaking. Gotta start somewhere....

    Denis

    PS: They do rest on the de-energized chuck with the tooth side elevated as desired.

  9. Likes jhruska, Paolo_MD liked this post
  10. #29
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Well I spent some time cutting in and then grinding to size the hinge. I ended up at .012" thick as that allows adequate flex---the teeth pop down when you turn on the magnet. I "sharpened" the teeth so they bite into the work. This might not always be desirable, but in th Is case, firmness of setup is the priority over appearance. I used a 7 degree relief angle so that when the tooth section is down flat on the mag you measure a 97 degree angle from the mag surface to the face of the teeth.

    While thinning the hinge with the grinder I did check periodically to see if a thicker hinge would work OK. My conclusion was that around 10 to 12 thousandths is the sweet spot (just like the commercial combs use) where it flexes well for the size of comb I am making but still seems stronger than I imagined it might at that thickness. I am not too worried about over bending it or snapping it. A heavier comb likely could use a thicker hinge. Maybe a 1/4" thick comb with a wider base and tooth segments might do fine at .015"or .018".

    I will post a couple more pics later and perhaps a 20 second video of the "snap-action" of these devices.
    I think these are going to work fine. I am indebted to all who have posted detailed info on this thread. It would have taken so much longer to get here without that crucial help.

    Denis
    Last edited by dgfoster; 12-04-2016 at 03:46 PM. Reason: typo. Thousandths not degrees

  11. Likes BillDe, michiganbuck liked this post
  12. #30
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Here is a link to a 60 sec video I made of the clamps responding to the mag chuck and clamping a part .:

    Comb Clamp - YouTube

    Denis
    Last edited by dgfoster; 12-04-2016 at 10:15 PM.

  13. Likes Paolo_MD, NodecoMachine liked this post
  14. #31
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    So, the mock-up clamp is done. Now I will use it for a while and see how it behaves. Then once I see how it fails and how it succeeds, perhaps a better one (and most likely a few different designs aimed for certain circumstances like roughing and finishing) can be made from parallels as suggested by Buck. One thing that seems like a possible improvement right off the top might be to make the teeth more tooth-like. That is to have more of a saw-tooth profile so they dig in more and hold even more securely. Or for more delicate work having "elastic" edges ( I think they meant rubber or plastic) as pointed out in the original patent 70 years ago for delicate work.

    But for now, having just gone through the process of making a first attempt, the parameters for successful design is more apparent and the potential for other designs come to mind.

    Here are a couple of pics I promised above.

    Denis




    Attached Thumbnails Attached Thumbnails comb-clamp-1-.jpg   comb-clamp-2-.jpg  

  15. #32
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    8,809
    Post Thanks / Like
    Likes (Given)
    2608
    Likes (Received)
    2989

    Default

    Nice job..

    I was going to mention when I got back in town to grind the opposite bottom to make the comb tilt up, but it looks like you figured that out.

  16. #33
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Quote Originally Posted by michiganbuck View Post
    Nice job..

    I was going to mention when I got back in town to grind the opposite bottom to make the comb tilt up, but it looks like you figured that out.
    Seemed like the easiest and most reliable way to get the job done. Thx.

    Denis

  17. #34
    Join Date
    Mar 2012
    Location
    Southern Wisconsin
    Posts
    539
    Post Thanks / Like
    Likes (Given)
    70
    Likes (Received)
    177

    Default

    I would make them with a separate piece of spring steel in a slot. But rather than trying to weld or silver braze them in, I'd just use red loctite. You have a ton of surface area and not much stress on the joint. It would be a permanent joint, unless you wanted to remove it. Also looking at the way they function, you could probably not even use loctite, as the action would hold everything together under the magnetic force.

  18. #35
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    3,709
    Post Thanks / Like
    Likes (Given)
    890
    Likes (Received)
    1857

    Default

    Quote Originally Posted by dgfoster View Post
    Snip>

    If the combs were a rarely used item, a person might get by making a bare-bones setup in two separate parts for each side. It would be fiddly, but would work I think to just skip cutting in fingers and just cut the bite angle on the narrow face of say a 5/8" parallels. Then roll up a tiny balls of aluminum foil ( or a bit of rubber band, soft thin packing foam etc) and put one near the part on each side. Now butt the 5/8 parallels against the part and supported near the part by the foil ball. Then block in these parallels with another parallel on each side. Apply the mag, so the down-force and and wedging action occurs. Might be something to do for that rare one-off situation.

    Denis
    Quote Originally Posted by James Lederer View Post
    I would make them with a separate piece of spring steel in a slot. But rather than trying to weld or silver braze them in, I'd just use red loctite. You have a ton of surface area and not much stress on the joint. It would be a permanent joint, unless you wanted to remove it. Also looking at the way they function, you could probably not even use loctite, as the action would hold everything together under the magnetic force.
    Agreed.

    One of the variations I alluded to in an earlier post would be to just put a cove on one piece and a matching convex or notch and ridge arrangement and skip the hinge all together. An "upgrade" would be to put the two pieces together and then put a piece of duct tape over the "joint." The pieces would remain in correct relative position as parts were re-positioned or interchanged. Lots of ways to do it.

    Denis

  19. #36
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    8,809
    Post Thanks / Like
    Likes (Given)
    2608
    Likes (Received)
    2989

    Default

    Quote Originally Posted by James Lederer View Post
    I would make them with a separate piece of spring steel in a slot. But rather than trying to weld or silver braze them in, I'd just use red loctite. You have a ton of surface area and not much stress on the joint. It would be a permanent joint, unless you wanted to remove it. Also looking at the way they function, you could probably not even use loctite, as the action would hold everything together under the magnetic force.
    One could also drill the shims and the parts and rivet them together.. we used to anneal a to-drill-spot on shim stock with a Dremel using a dull drill or a point wheel. Yes one would need to make the .010/.015 (or so slot)

  20. #37
    Join Date
    Dec 2008
    Location
    Milwaukee WI USA
    Posts
    1
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Quote Originally Posted by BillDe View Post
    We use these type of magnetic hold down clamps a lot. Here are a few photos. These just have a groove ground through to a thin section to form the hinge. I don't remember where we got them, they are at least 30 years old. These are photos of 1/16" thick and 1/8" thick, we also have a few different widths. They are marked Metric Systems. Billhold-down1.jpghold-down2.jpghold-down3.jpg
    Hi All,

    I have a pair of these hold downs in great sharp. I would like to sell but have no idea as to what they are worth.


    img_9122.jpg

    Paul


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
2