Having trouble finding...

[steamer]

--Looking for a bidirectional variable speed footpedal control for
a 1/3hp DC motor but haven't been able to find much via google. Anyone got a
line on something like this for less than a king's ransome? PWM would be
nice but not required..

 

[Winston]

--Looking for a bidirectional variable speed footpedal control for
a 1/3hp DC motor but haven't been able to find much via google. Anyone got a
line on something like this for less than a king's ransome? PWM would be
nice but not required..

I bought one of those packaged with the motor today
for $22. at my local hardware store. Of course, I
will have to unpackage the control and integrate
it into a foot pedal, but I think I have a pretty
good start on it.

It's a drill motor.



--Winston

 

[Winston]

I bought one of those packaged with the motor today
for $22. at my local hardware store. Of course, I
will have to unpackage the control and integrate
it into a foot pedal, but I think I have a pretty
good start on it.

It's a drill motor.

It is a B&D DR350FD found in the 'cutout rack' at my
local hardware store.
<http://www.ereplacementparts.com/bl...r-electric-drill-parts-c-4167_4168_35042.html>

http://global.ebay.com/Black_and_Decker_60_Amp_38_in_Drill_DR350FD_NEW/220713628239/item

I pried the boot (Item 25) off the nose and removed items
16-21. This reveals a 12 mm shaft that will host a timing
belt pulley, once it is bored out from 3/8" ID or reduced
from 1/2" ID.

I took out the switch (Item 8) so that it can go into
the foot pedal (Not Shown). I simply spliced the
'hot' and 'neutral' wires from the power cord directly
to the matching wires going to the motor.

I left the 'reversing' mechanism in place. It is
a mechanical 'brush phasing' deelybob that I will
actuate manually.

Once modified, I will clamp the motor to my machine using
something like:
<http://www.gsegmedia.com/Book/videos
flash/electric_drill_motor_mount.htm>

I imagine I will replace the rheostat in an old sewing machine
control pedal with the drill switch.

http://cgi.ebay.com/Singer-Sewing-M...212?pt=LH_DefaultDomain_0&hash=item2eb29cfc14


--Winston

 

[steamer]

--Aha! Thanks; hadn't thot of that.. Gotta go to Harbor Freight
anyway today so will snag a drill or two..

 

[Jasen Betts]

It is a B&D DR350FD found in the 'cutout rack' at my
local hardware store.
<http://www.ereplacementparts.com/bl...r-electric-drill-parts-c-4167_4168_35042.html>

http://global.ebay.com/Black_and_Decker_60_Amp_38_in_Drill_DR350FD_NEW/220713628239/item

I thought $22 was a little cheap for a battery drill drill with a 250W
motor. (I'd expect closer to $220, )

The guy wants to control a DC motor powered from some unspecified
source.

I guess if the mains voltage is suitable, and the motor insulation is
sufficient he could put a bridge rectifier after the drill speed
control circuit, there's a lot of if's there.

 

[Winston]

Jasen Betts wrote:

(...)

I thought $22 was a little cheap for a battery drill drill with a 250W
motor. (I'd expect closer to $220, )

I'll take that 'Official CSOB badge' now.

The guy wants to control a DC motor powered from some unspecified
source.

At an unspecified voltage and speed, too.

I figured Steamer was expressing a general need for

= 250 W of rotary motion, controllable WRT speed and

direction; using a D.C. motor as an example.

If he had a particular D.C. motor in mind, I would
expect that he would have mentioned a make and model
or at least a voltage, hence my 'conclusion leaping'.

The foot pedal is useful for drill presses and coil
winders, so I figured that either way, an intervening
gearbox would be a welcome addition.

I guess if the mains voltage is suitable, and the
motor insulation is sufficient he could put a bridge
rectifier after the drill speed control circuit,
there's a lot of if's there.

The motor in the B&D DR350FD drill is 'universal
brush type' and runs fine on D.C., so no further
rectification is necessary.

Steamer figured this was a good answer, so I
warn't too far off.

--Winston

 

[steamer]

--Just thot I'd explain the project a bit; I'm wanting to build a
rotary table for welding round stuff. With TIG both hands are busy doing the
welding and one foot controls power, leaving one foot free to control
rotation of stage. These units can be store-bought but prices start around
$1k and go up from there. I'm wanting to build my own, debug it as best I
can and call it done. There are issues with bearing wear when grounding the
torch and other weld power supply issues can screw with electronics so I
want to keep with the idea of cheap and easily replaced components..

 

[Jamie]

--Just thot I'd explain the project a bit; I'm wanting to build a
rotary table for welding round stuff. With TIG both hands are busy doing the
welding and one foot controls power, leaving one foot free to control
rotation of stage. These units can be store-bought but prices start around
$1k and go up from there. I'm wanting to build my own, debug it as best I
can and call it done. There are issues with bearing wear when grounding the
torch and other weld power supply issues can screw with electronics so I
want to keep with the idea of cheap and easily replaced components..

Slip ring on the table ?

Jamie

 

[Winston]

--Just thot I'd explain the project a bit; I'm wanting to build a
rotary table for welding round stuff. With TIG both hands are busy doing the
welding and one foot controls power, leaving one foot free to control
rotation of stage.

How about multiple carbon brushes in contact with an axle
underneath a 'ground plate' in a 'potter's wheel' config?

http://www.astrocalculator.com/Potters_wheel.htm

The central pipe holding both bearings could 'float'
electrically so that no current ever flows through
them.

--Winston

 

[Rich Grise]

--Just thot I'd explain the project a bit; I'm wanting to build a
rotary table for welding round stuff. With TIG both hands are busy doing
the welding and one foot controls power, leaving one foot free to control
rotation of stage. These units can be store-bought but prices start around
$1k and go up from there. I'm wanting to build my own, debug it as best I
can and call it done. There are issues with bearing wear when grounding
the torch and other weld power supply issues can screw with electronics so
I want to keep with the idea of cheap and easily replaced components..

I sit in a fab shop - they've got rotary tables on one side (machining), and
positioners (welding) on the other. I've sometimes quipped, on one side,
they take little pieces of metal and stick them together to make big pieces
of metal, and on the other side, they take big pieces of metal and cut them
up into little pieces of metal. Ha, ha, ha.

I'm pretty sure the positioners have motors to rotate them continuously,
but I can't imagine why you'd want to do such a thing, unless you're welding
something cylindrical.

Do you have access to a machine shop? I'd take some kind of post that will
take a thrust bearing, and it just occurred to me - go to the local auto
salvage, and get a flywheel and pinion, figure out how to mount a motor,
and use any ordinary speed controller.

For grounding, maybe use starter brushes?

Good Luck!
Rich

 

[Jasen Betts]

--Just thot I'd explain the project a bit; I'm wanting to build a
rotary table for welding round stuff. With TIG both hands are busy doing the
welding and one foot controls power, leaving one foot free to control
rotation of stage. These units can be store-bought but prices start around
$1k and go up from there. I'm wanting to build my own, debug it as best I
can and call it done. There are issues with bearing wear when grounding the
torch and other weld power supply issues can screw with electronics so I
want to keep with the idea of cheap and easily replaced components..

get some of that heavy duty copper braid used for earthing automobile
engines connect your welders work cable to that only and wrap it
once round the shaft perhaps with a spring to keep it taught.

http://www.gacopper.com/Braid.html

it says the biggest one's only good for 120A so you'll probably need several in
parallell.

(I saw a similar setup used for welding balance weights onto
driveshafts while they were on the balancing machine)

Don't give the current a chance to flow through the bearings,
so, if the welder is also used with a bench don't provide a
current path from the bench to the base of the turntable.
(or just insulate the bearings)

that way if your turntable's work contact fails the welder just stops
there's no secondary earth path possible.

 

[steamer]

Do you have access to a machine shop? I'd take some kind of post that will
take a thrust bearing, and it just occurred to me - go to the local auto
salvage, and get a flywheel and pinion, figure out how to mount a motor,
and use any ordinary speed controller.

--Oh yeah I've got a machine shop no problemo. We started messing
around with the worm drive motor assemblies yesterday and the first thing we
discovered is that they rotate waaaay too fast even at their lowest speed.
This means I'll have to mount the assy to a plate, then add a second shaft
parallel off to one side and then I can connect the two with timing pulleys
and a belt. By isolating the slower shaft with, say, delrin bushings I can
isolate it, electrically, from the motor assembly so that solves the
scrambling-the-electronics issue.

For grounding, maybe use starter brushes?

--Hey that's a neat idea! I'm thinking, tho, that if I limit
rotation to one turn, which is all that's needed for a weld, I can just put
the ground clamp on the shaft stub that hangs below its mounting plate.

 

[steamer]

--Addendum to addendum: finally did the math and looked up some
parts in the SDP catalog. They don't sell cog pulleys in enough variation to
do a pair of 10-to-1 gear reductions to yield 100-to-1 output reduction.
Best I could figure, with their parts, I could do something like 6-to-1
twice then maybe 3-to-1 once which makes for a very complex and large-ish
assembly with three timing belts and it ain't cheap: just the gears work out
to $55.- and then there are the belts. Shafts and mounting plates I could
make but it'd be a hassle.
--Have decided the easier way to go about this is to use my Sherline
cnc rotary table with a timing belt attached to the chuck; then I can add a
second electrically-isolated shaft off to one side, connect to it with a
timing belt and I'll be in business with precise control of rotation degree
and rate. Still have to figure out some sort of footpedal to control both;
hope to noodle on that with a couple of E-E pals who are coming to visit the
shop today. Stay tuned..

 

[Winston]

--Addendum to addendum: finally did the math and looked up some
parts in the SDP catalog. They don't sell cog pulleys in enough variation to
do a pair of 10-to-1 gear reductions to yield 100-to-1 output reduction.

I had this fantasy about gluing an inside-out cog
belt to a flat belt pulley to make my own custom
cog pulley.

I wonder if that would work?

--Winston

 

[steamer]

--Hey that's a neat idea! better be a damned good adhesive tho.. ;-)

 

[Winston]

Winston wrote:

--Hey that's a neat idea! better be a damned good adhesive tho..
;-)

I ain't so sure if Maximum Strength Gorilla Glue
is needed. The inside-out belt would be under some
smallish shear stress along it's circumference
and that is about it.

If it were a moderate press-fit to the pulley,
wouldn't it adhere at least as well as does a
band-saw tire, for example?


--Winston

 

[Winston]

I ain't so sure if Maximum Strength Gorilla Glue
is needed. The inside-out belt would be under some
smallish shear stress along it's circumference
and that is about it.

If it were a moderate press-fit to the pulley,
wouldn't it adhere at least as well as does a
band-saw tire, for example?

Er. Nevermind!

I tried it. The belts go 'out of phase' instantly.
Oh Well!

--Winston

 

[Jasen Betts]

I had this fantasy about gluing an inside-out cog
belt to a flat belt pulley to make my own custom
cog pulley.

the tooth profile is not right for use as a rigid cog.
that'll cause impulses as each tooth engages