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Type of motor to grind

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#1 Nebulae

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Posted 08 December 2012 - 10:37 AM

Hello everyone, i am back again. :cool:
I want to grind my 8" mirror with homemade grinding machine. So can you tell me what type of motor do i need and at what speed?
Can cooler motor will work?

your help will be appreciated :bow:

#2 Gary Fuchs

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Posted 08 December 2012 - 12:27 PM

Are you looking to do it as inexpensively as possible?

What do you mean by "cooler motor"? Air conditioner, refrigerator?

Gary

#3 kfrederick

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Posted 08 December 2012 - 12:28 PM

If You check ebay some times you can get a 90 deg gear drive DC motor with a speed control for not too much . 0 TO 40 RPM is what I use my turntable mounts direct to the gearbox one inch shaft . I got mine for 100 dollars .Sands Machine has aluminum disks that work good as tooling and turntables. For a 8 inch polishing by hand is not hard a lot of work making a machine for one mirror

#4 Steve Drapak

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Posted 08 December 2012 - 12:36 PM

Dennis at www.mirror-o-matic.com specifies a motor from Johnstone-Grainger, part S88-532 3K771, 1/4 hp, 1725 rpm, 48/56 frame. He lists it at $78

#5 Norm Meyer

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Posted 08 December 2012 - 01:15 PM

Hi,
How much grinding do you plan to do? I think
the fastest,at least for me,has been the tub grinder.
The nice thing is you only need one motor and that is
for the spindle. The overarm is hand controlled no motor
needed, but you have to sit there while grinding. I put a
DC motor to drive spindle to simplify speed control but it could be done with step pulleys. The DC motor is controlled
by a bridge rectifier and variac. I recently modified the
tub grinder so I could use it as a fixed post grinder like
Gordon Waite's as seen on You Tube. So basically it is two
machines in one. As far as motors if you can afford the DC
motor I think that is best. If you are not going to grind
more than one or two mirrors the cost wouldn't be justified.
I've used as little as 1/4 HP could be even smaller if it has enough torque. As far as speed somewhere around 20 to
40 RPM especially for grinding. Too fast and you'll throw off most of the grit. Go on You-Tube there are plenty of
grinding/polishing machine examples that's where I got the
idea for fixed post grinding. The old timers mostly recommended under 5 rpm for the turn table and maybe
30 strokes a minute.
Also check out Burden's Surplus in Nebraska they sell all
kinds of neat stuff for building machines.
Hope this helps
Regards Norm

#6 mark cowan

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Posted 08 December 2012 - 10:26 PM

Yeah, you don't need that much power on the motor for grinding, more for polishing. And keep the speed to about 40 rpm or below. I designed my original machine to run at 42 rpm from a standard 1/3 HP AC motor, which works great up to 20", but after replacing several pulleys I'm not sure what speed the table is. ;) There's a lot of latitude.

The new ones I'm building for up to 28" use surplussed DC treadmill motors run by a Variac (AC auto-transfomer) feeding a 25 amp bridge diode for 0-40rpm at 50v or so... I figure it makes around 3/4 HP there. Put a filter cap on that DC unless you want the motor to hum. :lol:

Best,
Mark

#7 Nebulae

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Posted 09 December 2012 - 01:12 AM

but what type of motor do i need?

#8 mark cowan

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Posted 09 December 2012 - 07:54 AM

There's no single answer. Any motor (DC or AC) will need a way to reduce the speed down to the speed you want for the spindle - this is either going to be done by a gear reduction or by a set of pulleys, and if pulleys, it takes more than one stage (1175RPM to 40RPM or so). Check out info on the Mirror-O-Matic (MOM) grinding machine online for a pulley approach.

Rather that starting with the motor you might want to decide on how to build the machine itself first...

Best,
Mark

#9 Nebulae

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Posted 09 December 2012 - 09:05 AM

Thanks friend
can this one will work ?
http://www.ebay.in/i...-/3210313092...

#10 ed_turco

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Posted 09 December 2012 - 11:23 AM

You really need an AC motor and a footswitch as an accessory if you sit down for your work. For smaller mirrors, 1/4 HP is plenty. You will have to get a suitable pulley system to get the RPM down to 30 or so, but I am using a pulleyed direct drive system.

#11 Gary Fuchs

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Posted 09 December 2012 - 01:56 PM

That motor looks much too small.

#12 mark cowan

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Posted 09 December 2012 - 04:43 PM

It looks too small. How about an old sewing machine motor? They have foot pedal speed controls and run off line voltage.

Best,
Mark

#13 danjones

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Posted 10 December 2012 - 12:15 AM

for trepanning blanks, i built a maching using an ac 1/3 hp motor to run it. i used pulleys. the motor was driven by a belt to a 12" or 14" pulley (i'd have to measure it) with a 4" pulley attached to the top of it. another belt from the 4" running to another 12 or so inch, which ran the cutter head. it resulted in about 30-35rpms or so. I tore down the cutter and am now melting blanks in a kiln, but am also building now a grinding maching which you speak of. I am using the motor (1725 ac) to run it. i'm just using pulleys to reduce the speed for the table. i'll make it easily accessible to swap out a pulley to change speeds when needed. I bought the motor from Craigslist for $20. I'm using a big wooden box, the motor, some belts, couple shafts, bearings, belts n pulleys, with a turntable on top. figured let's keep it simple and cost effective. i'm using a surge protector with on/off switch, swap a pulley when needing to change speeds. I like z6film on youtube for his machine. good luck.

#14 Nebulae

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Posted 10 December 2012 - 12:36 AM

Finally i decided to grind with my hand, as it is too complicated to build

#15 Paul Drufva

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Posted 10 December 2012 - 05:31 PM

for such a small mirror why bother with the expense and time in building a machine? It's all easily done by hand.






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