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  1. #31
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    Quote Originally Posted by Michael G View Post
    If you are going to secure a joint against shearing strictly speaking you should use a dowel pin (solid). I doubt that a roll pin would shear consistently enough to be used in a critical application.
    A Dowel pin is fine, just a little harder to do. In this case we don't care about consistent shearing, we want no shearing so I dont see an issue with a big ass roll pin(though a dowel pin the same size would be even better). I'm just wondering what Joe and Simon mean by shear pin? (roll pins was just my first guess.)

    Stuart

  2. #32
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    Talking about questions for engineers. Looking at the pivots points for the hold down clamp and cam of Bobs folder from the forum design.
    Wouldn't it be "nicer"(if possible) to either bring the top pivot forward or take the cam pivot backwards?

    Or am I worrying about nothing and making up problems(likely as the thing works as is)

    Stuart

  3. #33
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    Thanks guys. Wrt pins. Yes I eeally meant dowel pins not shear pins. I remember Michael telling me that bolts should not be used to hold shear forces. I have a few options..... (1) ignore the advice and use maybe 4 bolts each side. (2) weld a strip of heavy steel for the flange end to rest on and take the stresses and then use bolts for clamping as per recommendation. (3) As per Joes advise. Bolt together and then drill and press fit some pins wach side. (4) weld the whole thing together.

    Im leaning towards 2 or 3....

    WRT the cam hold down and pivot point. I feel there would be maximum leverage achieved if the clamping forces are vertically downwards with no diagonal component. Also want it as close as possible to the end of fingers to reduce (or increase) the leverage. Was thinking about these exact issues yesterday and thats what I decided.

    Michael. Drilling the holes was no joy and certainly not why I bought a mill but the end justifies the mean in much of what I do. As long as it does no damage to the machine and its no unsafe, I will go to extraordinary lengths to achieve results!

    No colour has been choosen yet Stuart. That would be getting ahead of myself given the work still to be done. Hopefully the hinges and endplates will be the most difficult parts given their size.....

    Simon

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  4. #34
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    Hi Bob,

    I meant to say earlier today that the design by Simso http://www.woodworkforums.com/showth...folder+fingers
    inspired me to investigate further and then finally take the plunge to make my own. I must have read that thread 2 -3 times over! A very comprehensive thread with pics and plans. I then decided to make it 900mm based on my materials I had and thanks to Michaels help with his pics. Then, about a month ago I decided to make it 1200mm. However, going from 900 to 1200mm has incurred some extra expense due to lack of suitable materials. I would ultimately like to have made a folder where the capacity of steel that it bends (folds) is limited by your own strength, not the folder itself. However, after some research and looking at folders in H&F and google images of folders, it becomes very clear that the forces involved in bending or folding soon add up with width and metal thickness to the point where the weak point will always be the folder and not the person using it! So, I have made things as heavy as possible with my materials, and I will take pleasure in seeing what it will do.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  5. #35
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    Not sure why the reluctance to use bolts in shear?
    High tensile bolts are regularly used in shear very effectively. The portal frames in many large buildings, earth moving equipment and mechanical applications are just a few examples. I would wager that a high tensile bolt is probably a higher grade material than most dowel pins.

  6. #36
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    Quote Originally Posted by Karl Robbers View Post
    I would wager that a high tensile bolt is probably a higher grade material than most dowel pins.
    I sure wouldn't.....

    Dowel pins are up around 60 Rockwell C, and are made from steels like 4140 or 100CR6
    Grade 8.8 bolts are anything from 20-30 Rockwell C, are made from medium carbon steel and have weak points built in to them....

    Simon, nice work.
    I would but some dowels in if you could fit them.

    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  7. #37
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    You learn something every day.
    I've never been particularly impressed by 8.8 bolts as far as their HT properties and for a critical application would always use 10.9 or 12.9 metric bolts or Grade 8 CATERPILLAR bolts which surpass the SAE standard by a fair margin.
    Where abouts is the inbuilt weak area on a HT bolt?

  8. #38
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    Bolts have a built in stress raiser because of the thread, especially where the it transitions from thread to smooth shank. If they are not treated correctly they can take on hydrogen and become more brittle too. Bolts with rolled threads are better but it is still there
    Engineering theory is that bolts are used in tension to increase the friction between two surfaces - so strictly speaking you are not using the bolt in shear but in tension and the things you are bolting together are acting in shear but because of the resisting forces, don't. In reality lots of people (including me) use bolts that are effectively in shear but it is regarded as poor practice. I once made the mistake of suggesting using bolts in shear to an aircraft engineer and let's just say that I remember that it is not the correct way of loading a bolt now.

    Michael

  9. #39
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    Hi guys,

    So, dowel pins it is. In truth I didn't know they were specific item, I thought they were just machined up out of steel and then fitted. Then by use they are called dowel pins!

    OK. So I'm learning stuff! If I was to have a wild guess I would choose maybe two dowel pins each side. Maybe 3/4" ? Being high tensile, there will be little room for error, not sure if you can fit a (say) 3/4" dowel pin with a 3/4" drill bit. That would be too simple I'm thinking and create a loose fit. Will I need to drill or bore to close and then finish with a 3/4 reamer?

    Hi Michael, thanks for the explanation on the bolts. As my kids would say, your mind is full of stuff!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  10. #40
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    OK. How about 2 x M16 dowel pins on each side and clamped together with 4 M12 bolts each side? Overboard or not enough?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  11. #41
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    Quote Originally Posted by simonl View Post
    How about 2 x M16 dowel pins
    You have threaded dowel pins? Blame RC, he started it

    Do you have a 16mm reamer? or can you get it all on the mill?

    Stuart

    *ok granted you can get threaded dowel pins but I'm pretty sure Simon means 16mm not XXdia with an M16 internal or external thread for removal.

    p.s. "bolts" can be used in sheer but becomes a designed joint. With the threaded section removed from the sheer interface. So it really becomes a pin with a thread on the end. They are made, I just cant remember their name ATM. Now whether they do the job as well as a separate bolt and pin I cant say. The thread is smaller than a normal bolt so you might not be able to get the correct preload. There really is much more to it. Pins can made from things bolts cant be......But then..... most of use aren't building airplanes of race cars...still an interesting subject none the less.
    Last edited by Stustoys; 28th Mar 2014 at 01:49 PM. Reason: p.s.

  12. #42
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    Hi Stuart,

    WRT M16 dowel pins, I only called them M16 after doing a search and noticing that's what everyone who sells them were calling them! Examples:

    https://www.fastenersclearinghouse.c...L79FE9A851111;
    http://www.theboltbin.com/index.php?...roller=product

    See! so don't shoot the messenger!

    Anyway, went to the local bolt place and bought 4 M<16 x 50mm dowel pins for about $20. Don't know if I have a 16mm reamer. Can't remember, I'll have a look. Would be nice to line it all up and do it on the mill. I assume I can still do it on the mill with a reamer as long as I don't move the table after making the hole? I'm not sure if I can make a 16mm hole with my boring head, it may be a little too small. Have a look later. Off the top of my head, I'm thinking a 5/8 drill bit to get me started….. I have one of them.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  13. #43
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    Well, I have some reamers. None of which are metric and the largest size is 1/2"! But I have a cutter for my boring bar that is capable of approx 15mm hole. Looks like thats the go at this stage. Also just occurred to me that I not "locked in" to using the supplied cutters anyway. I can always make my own HSS cutter just for the job. More than one way to skin a cat I guess…..

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  14. #44
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    Quote Originally Posted by simonl View Post
    WRT M16 dowel pins, I only called them M16 after doing a search and noticing that's what everyone who sells them were calling them! Examples:
    Well that'll learn me!
    I guess I shouldnt be surprised there is an M spec for dowel pins.

    Stuart

  15. #45
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    Quote Originally Posted by Stustoys View Post
    Well that'll learn me!
    I guess I shouldnt be surprised there is an M spec for dowel pins.

    Stuart
    Well, I may have only learnt that a few hours before you but I can still claim to have taught you something Stuart!

    Only took 3 years….

    Simon (aka Grasshopper )
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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