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8th April 2014, 06:40 PM #1
3 way lock, engineers or others help please
Will this work, you will need to look at the pic
I want to lock a sliding block "A" against rails "C" 1&2 so that it will not slide.
At the same time I want to lock beam "B" against block "A" so that it will not slide
Both need to be able to move readily when not locked but be able to be locked to with stand strong human pushing preasure. Other than what you or I could move with our bare hands there is no other particular pressure to cause movement.
I am imagining a cam lock pulling down where the middle arrow is. A block would would simultaneously pull down on each pivoting break onto the "C" tubes.
Looking at the pic again I think I need to have a pulling between the pivoting blocks and the clamp on the "B" block otherwise one may lock before the other. So more like the pic below, perhaps a sliding wedge operated by a cam underneath.
Ideas and views appreciated.
Dave the turning cowboy
turning wood into art
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8th April 2014 06:40 PM # ADSGoogle Adsense Advertisement
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8th April 2014, 07:03 PM #2Senior Member
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Dave,
I think you have all of the elements for success in your second sketch, just needs a bit of fine tuning of dimensions and angles to make it work, and I think you will not need complicated pivoted parts. It should be possible to make it all lock up together, and all come free when the lock is released.
If you can give an idea of the dimensions and materials of the parts to be clamped it would help to rough out a solution.
Cheers,
Bill
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8th April 2014, 07:44 PM #3
G'day Bill,
Quicker to sketch with dimensions. As you see below.
My biggest concern would be if the break blocks against the round bar were to not come free easily.
There are some other details to the block as well, first is fine tuning the lock mechanism.
I want to have new tubes with slots / teeth like you find on the back of a drill quill so I can have a wheel to advance this back and forth along the tube.
I do not know how deep the slots need to be or who much thicker the tube needs to be to compensate for the slots
The block would have two sets of holes in the other direction perhaps about 22mm, one set to operate the cam lock and the other to have a geared spindle to advance the block along the tubes. I would want the gears to be such that it will spin freely if pushing by hand but strong enough to advance with a hand wheel if I desire.
thanks
Dave the turning cowboy
turning wood into art
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8th April 2014, 08:48 PM #4Pink 10EE owner
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Only problem I could foresee is one may still lock and the other not be loose but not locking as tight, due to not enough friction.... And if you tighten more something starts to warp or bend...
Also you have to have it so the wedge on the round bar will unlock and not jam...Light red, the colour of choice for the discerning man.
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8th April 2014, 08:54 PM #5
How positive does the rack drive need to be? It would probably be a lot easier to achieve a cranked drive with a rubber wheel machined to match part of the profile of the rail and maintained under moderate pressure. Avoids having to cut a rack in the rail and match it to a gear. Definitely would not be as positive as a drive system, but should not be an issue for a hand crank.
Another possibility for a simple drive that is a bit more positive than a friction drive would be a small winch drum on the cranking shaft holding 5 or 6 turns of heavy SS fishing trace (300lb braking strain or similar) with the line secured and tensioned at locating blocks at the end of the rails. (Can sketch out if needed)I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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8th April 2014, 09:10 PM #6
Its a tricky bit of engineering Dave. My thoughts are that in your first sketch I think that that could work but your second sketch, to me. I don't think it will. It looks like your wedgy bits are upside down ie if you jam the round rails the tee slotted beam won't get clamped. I think that you may not have enough movement to grip the rails and the tee slotted beam. My reasoning is that the Tee slot won't offer much vertical movement compared to the movement necessary to grip the tubes. But as I said its just my way of looking at it.
Are you constructing a homemade Intercontinental Ballistic Missile??? Or maybe a Time Machine??? It can't be a Tardis (they have been done to death) I know your own satellite so we will be able to watch you playing with your lathe from the comfort of our own living roomJust do it!
Kind regards Rod
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8th April 2014, 09:45 PM #7
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8th April 2014, 09:53 PM #8
The second picture was done more roughly.
If you imagine the wedge mechanism as drawn in the top picture but under the rails instead of on top. Perhaps no pivot. The wedge can move freely on the shaft and a cam under the wedge. As the cam is turned the wedge is forced up and the 'T' on top is pulled down. This was both locks are (or all three) are activated with the one action.
It is actually an old lathe which I am trying to renovate and bring into this generation of workability.
I am not sure if I should modify the existing block or try and find something big and solid that can be machined to my specifications.
Dave the turning cowboy
turning wood into art
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8th April 2014, 10:37 PM #9Senior Member
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Concept sketch
Dave,
I have sketched a concept using a single wedge block that loads against the two round bars (tubes?). Note that the wedge block is a single piece with a central hole for the clamping bolt.
The relative locking effect on the bars vs the t-slotted part at the top is controlled by the wedge angle and would need some experimentation in practice, but the good news is that the only part that would need changing is the wedge block. I expect that if the wedge angle (on each side) is more than 5 degrees the wedge will not be self locking, but if you wanted a very 'clean' unlock you could fit a spring above the wedge block.
Concept sketch.jpg
As you can see, you can not tighten one part without a similar load being applied to the other, and when one part is loose the whole lot is loose. To get that working nicely think all you need is to have a close (but not tight) fit between the clamp bolt and Block A, and plenty of clearance between the clamp bolt and the wedge block. That allows the wedge block to rock a little and/or float sideways to make contact with both bars so they will both lock at once. As mentioned above, the angle of the wedge will control the locking force in relation to the clamping load applied by the cam mechanism.
One aspect that may need consideration is damage to the round bars caused by loading by the faces of the wedge block. Probably the easiest fix (if there is a problem) would be to make the wedge block of a softer material than the bars eg. steel bars and a wedge block with brass faces (or an ironwood wedge block?).
Cheers,
Bill
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8th April 2014, 11:04 PM #10
Bill,
That is great. I was just considering how I would hold two independent wedges in place as I was emailing a mate in the states. I was thinking brass but even timber could work. The other thing I was thinking was to cut the wedge with a curve to match the curve of the bars. Especially with timber this would probably work better.
Had not thought of timber either.
thanks
Dave the turning cowboy
turning wood into art
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8th April 2014, 11:33 PM #11Senior Member
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Dave,
I did think about that. In effect the curve would give you a variable wedge with rather unpredictable results in terms of clamping effect I would imagine.
If your concern is concentrated loads where the wedge meets the bar, it may be better to have curved shoes (curved to match the bars) that sit, and can slide a bit, on the wedge faces. Just a thought.
Cheers,
Bill
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9th April 2014, 12:03 AM #12
Bill
that makes sense, if I go the tiimber option even a straight wedge is not going to cause any grief, may start with timber and go form there, can experiment a lot that way
Dave the turning cowboy
turning wood into art
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9th April 2014, 12:33 AM #13.
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I think It could be made even simpler.
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9th April 2014, 12:58 AM #14
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9th April 2014, 01:27 AM #15
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