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'[OT]: Mechanical question'
2002\04\30@131214 by Sean H. Breheny

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Hi all,

I'm trying to connect a drive shaft to a piece of aluminum plate. The way
I'm attempting to do this is to pass the shaft through the plate at a 90
deg angle. The shaft has a keyway in it and I'm going to make the hole in
the plate have a small tab that will fit into the keyway. I need to find
out how much torque can be applied before the tab will break off. I know
this probably has something to do with shear strength (and will involve the
dimensions of the keyway, diameter of the shaft, properties of the
aluminum, etc.) but I don't know what method to use to figure this out.
This is only a hobby project so all I need is a reasonable estimate. Can
anyone help me out?

By the way, the project (rotating platform for the antenna of my weather
radar project,
http://www.rocket-roar.com/BT/wsr.html ) DOES have several PICs in it, so
this is at least remotely connected ;-)

Thanks,

Sean

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2002\04\30@141537 by Lawrence Lile

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Two recomendations:

1.  Build it a lot bigger than you think it will ever need to be.  Then
don't worry about torque.

2. Build a small simulated aluminum plate with a tab, and torque it with a
torque wrench until it breaks.

3. (Bonus)  Forget the aluminum tab, unless your plate is very thick this
seems like a weak spot.  Use some steel collars with real keyways, use steel
keyway inserts, and bolt through the steel collars to trap your aluiminum
plate.  Then don't worry about the torque, it'll be big.

--Lawrence

{Original Message removed}

2002\04\30@142158 by Sean H. Breheny

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Hi Lawrence,

Thanks for the quick response. The problem with #1 is that I don't really
have the right tools to do this kind of stuff so I am limited in how thick
a plate I can really drill and work. The problem with #2 is that I don't
have a torque wrench (but I guess they are not that expensive so I should
probably buy one anyway) and also the drive shaft has no "head" on it that
can be grabbed by a wrench.

#3 is interesting and I thought about that, but I had some trouble finding
collars with holes in them that could accept bolts. I am using
McMaster-Carr as my supplier. Can you point me to such beasts?

Sean

At 01:12 PM 4/30/02 -0500, Lawrence Lile wrote:
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2002\04\30@145143 by John Ferrell

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If the shaft has a keyway there must be a pulley,roller,sprocket or gear
that fits on it. Use that and bolt (JB Weld?) the plate to it.

{Original Message removed}

2002\04\30@165055 by Peter L. Peres

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Hi,

I think that I would use a steel disk bored to fit the shaft and bolted to
the aluminium base. I might use two steel disks (one on top one below) and
through bolts. Think pipe flanges bolted on imho. The keyway could be
engaged by a steel pin that would fit into a machined rectangular hole in
the aluminium plate, and be sandwiched by the steel plates. The reason I
say this is, that aluminium is maleable and will not hold its shape around
the shaft, it will develop play rapidly.  This will also make it easier to
machine things I think, you would only need a drill and a metal saw that
fits the round hole to make the elongated hole for the pin. The pin could
be a matching drill bit's shaft (to match the keyhole). You can stack
several pins in the slot if the aluminium is thick enough.

Maybe you can get away with just one steel plate. You do not say if this
is load bearing (axial, bending, etc). Imho think pipe flange. I saw your
radar pages and I wish you good luck. If I'd have to do it I'd visit an
auto scrap yard and buy a wheel with its semiaxle and bearing (not a
driven wheel), take it to a welder and have the semiaxle welded to a base
made of another wheel without its axle and bearing (why not) or some
suitable sturdy base, like a tripod made of 3 short 1.5" pipe segments.
Then I'd build everything on the moving platform on the now horizontal and
free spinning wheel. This is a good quality low friction and low play
bearing that can take about of ton of axial force without too much trouble
and still turn easy.  This trick has been used before to mount antennas
and telescopes.

hope this helps,

Peter

On Tue, 30 Apr 2002, Sean H. Breheny wrote:

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2002\04\30@165059 by James Paul

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Sean,

Go to the Home Depot and pick up a couple Rail Stantions.  They are
about 4" in diameter and have a 1" or so hole in the center and 4
screw holes around the circumference.  I used two of these on a wood
and aluminum platform that I used to hold up a "V-Beam" Antenna for
10 meter ham use.   That was about 5 years ago, and the antenna is
still working like a champ.   I did a little modification to them
before I put them into service though.  I drilled and tapped an angled
hole in the base near the center hole.  When I slid the mast through,
I put a machine screw in the hole and engaged the mast to keep it from
slipping.  I did this to both of them.  I put one on each side of the
frame assembly and put them so the tapped bot holes were 180 degrees
apart.  Bolted them into place and as I said before, they are working
fine after 5 years or so of service.   The best part about it is they
were only a couple of dollars each.  The tap I already had as well as
the machine screws.   If you bought everything new, you should still be
able to come in under 10 bucks.  Not bad I do believe.

                                                 Good luck.

                                                   Jim

 P.S.  Let us know how you make out with it.




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2002\04\30@181232 by Lawrence Lile

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I'm wtih Peter Peres on this one - pipe flanges work just about like I
described.

--Lawrence

----- Original Message -----
From: "Sean H. Breheny" <@spam@shb7KILLspamspamCORNELL.EDU>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Tuesday, April 30, 2002 1:19 PM
Subject: Re: [OT]: Mechanical question


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steel
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2002\04\30@193029 by Bob Ammerman

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> 3. (Bonus)  Forget the aluminum tab, unless your plate is very thick this
> seems like a weak spot.  Use some steel collars with real keyways, use
steel
> keyway inserts, and bolt through the steel collars to trap your aluiminum
> plate.  Then don't worry about the torque, it'll be big.
> --Lawrence

This also has the advantage that it will be much easier to drill a round
hole in your plate than to punch out one with a tab in it.

Bob Ammerman
RAm Systems

> {Original Message removed}

2002\04\30@200820 by Jim

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I know this is not the answer you were looking for but it would be stronger
if you cut a square hole in the
aluminum plate and inserted a piece of standard size steel key stock also
way easier than cutting a hole
leaving a square tab in it.

{Original Message removed}


'[OT]: Mechanical question'
2002\05\01@041359 by Alan B. Pearce
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>3. (Bonus)  Forget the aluminum tab, unless your plate is very thick this
>seems like a weak spot.  Use some steel collars with real keyways, use
steel
>keyway inserts, and bolt through the steel collars to trap your aluiminum
>plate.  Then don't worry about the torque, it'll be big.

You could always do this the reverse way by having a slot in both the
aluminium plate, and the shaft, and fitting a key that protrudes from the
shaft. This is known as a Woodruff key, and is commonly used on the flywheel
of lawnmowers and similar small petrol engines. The key is made of a soft
metal, so it will shear and protect things when the shaft is suddenly
stopped. You should be able to get a suitable key at a lawnmower repair shop
for pennies.

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2002\05\01@111346 by Sean H. Breheny

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Thanks to all who responded. I think I will take the suggestion to find
some component that is meant to mount on the shaft (like a sprocket, which
I can get for about $6) and then bolt that to my plate. I just bought the
shaft and associated hardware from McMaster and they arrived yesterday back
at my home address. I am going there this weekend and I will take a look at
everything to make sure it is what I expected and make a more definite
judgement on how to proceed.

Sean

At 09:12 AM 5/1/02 +0100, you wrote:
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2002\05\01@133313 by Jim

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I think you might find these people cheaper on machanical parts
http://www.useenco.com/



-----Original Message-----
From: Sean H. Breheny <EraseMEshb7spamCORNELL.EDU>
To: RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU <RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU>
Date: Wednesday, May 01, 2002 8:13 AM
Subject: Re: [OT]: Mechanical question


{Quote hidden}

this
>> >seems like a weak spot.  Use some steel collars with real keyways, use
>>steel
>> >keyway inserts, and bolt through the steel collars to trap your
aluiminum
>> >plate.  Then don't worry about the torque, it'll be big.
>>
>>You could always do this the reverse way by having a slot in both the
>>aluminium plate, and the shaft, and fitting a key that protrudes from the
>>shaft. This is known as a Woodruff key, and is commonly used on the
flywheel
>>of lawnmowers and similar small petrol engines. The key is made of a soft
>>metal, so it will shear and protect things when the shaft is suddenly
>>stopped. You should be able to get a suitable key at a lawnmower repair
shop
{Quote hidden}

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2002\05\01@135700 by Sean H. Breheny

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Hi Jim,

Thanks for the tip. I just checked them out. They do have cheaper prices on
some items, but for the ones that I have been buying (shafts, shaft
collars, flanged plain bearings, etc.) they seem to be very similar.

Sean

At 10:33 AM 5/1/02 -0700, you wrote:
>I think you might find these people cheaper on machanical parts
>http://www.useenco.com/

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