Do you have to use high tensile bolts in mill clamps?

Discussion in 'General Engine Discussion' started by spuddevans, Oct 20, 2008.

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  1. Oct 20, 2008 #1

    spuddevans

    spuddevans

    spuddevans

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    Hi there, this is probably a commanly known thing, but being a metalworking newbee I was just wondering, Do you have to use High Tensile threaded rod or bolts for use in clamping in the mill or rotary table?

    I ask as I am in the process of milling some T nuts for my Rotary table and the T slots are narrower than my mill table T slots, so narrow that I'm not able to use the M10 bolts and threaded rods in my mill clamping kit.

    I've been tapping my rotary table T nuts M8 but am wondering whether I can just use regular M8 threaded rod or does it have to be hardened or high tensile?

    I have got some M8 bolts in a clamping kit for my faceplate for my lathe that I can use, but they are not very long so I'd need to get some longer bolts / threaded rod.

    Thanks in advance for your help,

    Tim
     
  2. Oct 20, 2008 #2

    Maryak

    Maryak

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    Spud,

    I have found ordinary nuts and bolts to be more than adequate for clamping ;D

    Others may have different ideas.

    Regards
    Bob
     
  3. Oct 20, 2008 #3

    mklotz

    mklotz

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    If you manage to strip a common bolt while clamping on your mill or RT, you're doing something far more wrong than using less than super high strength bolts. :)

    Solid, reliable clamping with strap clamps depends far more on the geometry of the setup than on the strength of the bolts. Keep the bolt supplying the force as close as possible to the work, i.e., near the nose of the strap that rests on the part. That way most of the clamping force will be applied to the work and not to the packing supporting the back of the clamp and, as a consequence, you will need to tighten the bolt less to supply adequate clamping pressure to the part.
     
  4. Oct 20, 2008 #4

    spuddevans

    spuddevans

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    Thanks guys, I kinda thought that regular bolts / threaded rod would do, but working with metal is new to me and I've read that its important to have the workpiece firmly and safely clamped so just wanted to make sure before trying it out myself.

    I've read that before on this forum, I've been trying to get the bolt as close to the workpiece as poss', and have also found that having a packing piece as close as poss' to the same height as the workpiece gives a much better grip. ( I know that this is something that's obvious and automatic to you guys, but this is all a learning experience to me ;) ;) )


    Tim
     
  5. Oct 20, 2008 #5

    CrewCab

    CrewCab

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    Interesting question Tim, having runaged thro' mi bits n' bobs for clamping etc the only ones I can find which are marked are the ones cuttently holding the vice to the mill; and I believe thy came with the mill .............. they are marked as grade 4.8, now from the deepest darkest depths of my memories ??? .......... that's a standard "black bolt" or ordinary carbon steel, by comparison, grade 8.8 are high tensile and about twice as strong

    Having had a quick look in a very old text book it seems 2 x 10mm bolts (3/8") will take a bit over a ton in single shear and a little more in tension (these are safe working loads, not ultimate loads).............. so if we compare that to something we can visualise, two 3/8" black bolts should easily support Bernd's new milling machine ................ blimey tough little beggars ;D

    So, I would think they should be fine.

    hth

    CC
     
  6. Oct 20, 2008 #6

    rake60

    rake60

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    Over tightening clamping fasteners is a comman practice even the
    the professional machining field.
    If tight is good, tighter has to be better! ::)

    I am not familiar with the Europe standards for steel.

    Here, we have 2 comman grades of bolt and all thread.

    Grade 5 is a soft steel. It's fine for a low stress application where
    constant disassembling will not come into play.

    Grade 8 is made from 4140 alloy steel. It's much stronger and will not
    deform, pull or strip after multiple assemblies.

    Rick




     
  7. Oct 20, 2008 #7

    wareagle

    wareagle

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    Tim, I use regular hardware store bolts for clamping purposes and have never had a problem. As has already been said, the key is to have the bolts close to the work piece, and to use an adequate number of clamps to safely secure the work piece to the table.

    This hobby is a learning experience for all of us! The only dumb question is the one not asked!
     
  8. Oct 20, 2008 #8

    spuddevans

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    CRUMBS!!! :eek: :eek: :eek: :eek:

    I guess that begs the question, how do you know if you're over tightening a clamp? ( I think I know that the answer is going to lie in experience rather than anything that can be described over the medium of a interweb forum )

    I think that there is the same or similar two systems here.

    I guess that if you overtighten a normal ( ie non-high tensile ) bolt you'll only damage the bolt rather than potentially damage either the clamp or the table ( mill or rotary ) T slots.


    Tim
     
  9. Oct 20, 2008 #9

    rake60

    rake60

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    Tim it is a leaning curve.

    If we all tightened out clamps with a toque wrench we'd have a perfect answer.
    I don't know of anyone who does that.

    I do know that I have twisted, bent or indented clamp marks in many parts.
    I've also not had enough clamping pressure on parts, and had them move
    while machining them. Sometimes with rather dramatic results.

    There is no perfect answer.
    It is about personal perception of what is snug, tight or rock solid clamped.
    It becomes the feel of the hand pulling the wrench.

    Rick







     
  10. Oct 20, 2008 #10

    CrewCab

    CrewCab

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    Rick, while you and Spud are both here ;) ................. Tim raised a point in his "My Shop" threaad about concerning disengaging his X2 Mill taper / drawbar ................ I now "sucessfully" use a time honoured method I picked up on here ......... and I'm sure it came from you ........... the phrase went something like ............ "I just beat the drawbar with whatever spanner happens to be in my hand at the time" ............ or something along those lines ;D

    Anyway .............. it works great, the spanner is a Chinese open ended 17mm so not massive, and a couple of taps is usually all that's required .............. but mine's an R8 taper ............ is yours an MT3 like Spud's

    CC
     
  11. Oct 20, 2008 #11

    spuddevans

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    I have since took Tin Falcon's advice and have been a little more gentle with tightening the drawbar and I too can now release the MT3 with a tap or 2 from the chinese open ended spanner, although the chuck's MT3 seems to stick more than my 6mm collet and requires a little more effort.

    Tim
     
  12. Oct 20, 2008 #12

    CrewCab

    CrewCab

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    Glad you've got it sorted Tim, to be fair due to the lack of the recommended "copper hammer" I started with a block of wood and a "comfy" hammer ............ but Rick's wise words struck home ............ it's a lump of steel, so it can stand a little persuasion ;D

    Good luck, I'm on the same learning curve roller coaster ride and probably in the same carriage, only a seat or two in front 8)

    atb

    CC
     
  13. Oct 20, 2008 #13
    CC
    Theory is fine, not to be nasty but I sure as
    sh#$ wouldn't stand under Bernds milling machine
    suspended like that ;D
     
  14. Oct 20, 2008 #14

    CrewCab

    CrewCab

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    Blo**y Hell Paul ............. neither would I :eek:

    ;) CC
     
  15. Oct 23, 2008 #15

    tel

    tel

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    WIMPS
     
  16. Oct 23, 2008 #16

    DickDastardly40

    DickDastardly40

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    Further to the answers above, I would like to add:

    Once all your clamping bolts are tight give the clamped part, vice, fixture etc a damn good shake to prove it is secure.

    Just because the bolts are tight doesn't mean the job is firmly held especially if it is an odd shape or you have done up the left hand nuts before the right hand. Pull up the nuts diagonally oppposite similar to a flange or car wheel or if a long part start in the middle and work alternately outwards like a car cylinder head.

    Also give the clamped part a Mk1 eyeball underneath with the light the other side of the part and maybe have a poke around wth a small feeler guage to ensure you haven't canted it over and it is flat on the table.

    Hope this is of help to sombody.

    Al
     
  17. Oct 23, 2008 #17

    Dhow Nunda wallah

    Dhow Nunda wallah

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    For what it's worth..............
    my experience on small machines is, just tighten with one hand
    (one-eye tight)

    You won't break it and it won't fly across the yard ;)
     
  18. Oct 23, 2008 #18

    spuddevans

    spuddevans

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    That's good advice to check that the part hasn't canted over and is flat, I will check that from now on, Thanks mate,

    Tim
     
  19. Oct 23, 2008 #19

    rake60

    rake60

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    When I operated a large vertical boring mill the 4 jaws on the table were
    fastened to it with 4) 3/4" T-Bolts and Flanged Nuts.
    They HAD to be tight to keep the work piece from moving as well as
    avoiding centrifugal forces from throwing them off.

    I worked with two other operators on that machine.

    One was an older gentleman. When I'd remove the jaws I'd wonder how
    they ever stayed in place. They could be removed with one hand
    on the 3/4" drive ratchet.

    The other was a younger man who was easily twice my size.
    It wasn't uncommon to break a few of those 3/4" T-Bolts while
    loosening them!

    Tightened is different to everyone.

    Rick



     
  20. Oct 23, 2008 #20
    Tel
    I'm speechless, so speechless I had to tel you
    BR
     

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