Looking for suggestions on how to "grease proof" a synchronous motor (for food use)

bigpaul22 · Sep 14, 2017

Looking for suggestions on how to "grease proof" a synchronous motor (for food use)

Hello all

I'm looking for some advice on how to properly grease-proof a cheap Chinese-made synchronous motor.

Background: a few months back I invested in a vertical rotisserie to cook kebabs at home. It looks like this:

After a few months I noticed the motor would take several minutes to start spinning. I opened the unit up and found this ungodly mess:

That's the motor which drives the main rotisserie skewer. It's a cheap Chinese-made synchronous motor with a notch cut into the shaft. The food skewer has a protrusion which slides directly into the notch, and thus makes whatever food is skewered onto the skewer spin around.

The problem is that the motor unit is not sealed at all, so the grease and fat from whatever you're cooking drips directly down the skewer and straight on to (or in to) the motor shaft, resulting in what you see in the above image.

I've ordered a new motor to fit to the unit.

My question is: what's the best way to seal and grease-proof this unit when I fit the new motor? The skewer obviously needs to be able to spin around freely and needs to be able to be removed for cleaning, so I can't simply apply a silicone seal around the motor enclosure.

I've considered soldering the drip plate to the skewer so that there's no direct path from the skewer into the motor, however I'm concerned about the safety of having solder directly contact food, and also the unit is exposed to high temperatures which might compromise the solder over time.

Here are some mockups I made:

johansen · Sep 14, 2017

find a disk, epoxy/locktight/press fit it to the shaft so the grease is slung off the disk.

jdavi581 · Sep 14, 2017

Need the bottom plate removable with the skewer-welded or pressed on so all the drippings are captured, basically a plate with a skewer sticking out. Take it out to wash, no way to get near the motor and easily cleaned. I would roll the edges up to make the plate, and pierce the center of the plate and TIG or spot weld to the skewer. To seal with the heat with the existing design, ceramic seals are likely to be the only thing to take the heat.
Joe

Chip Chester · Sep 15, 2017

johansen said:
find a disk, epoxy/locktight/press fit it to the shaft so the grease is slung off the disk.

Not much slingin' will be happening at 1 RPM.

Permanent solution is to mount the motor outboard of the cooking area, and use a chain drive like on baking/breading equipment. Stainless sprockets. Wipers on chain return to motor zone. Clean nightly, per NSF rules. (<--- that's the kicker.)

If you decide to solder, use silver solder. Lifted from a DIY site:

"Your basic silver solder has a melt temp of no more than 750 degrees or so.

Brazing, Soldering, Welding, Cutting & Gas Distribution | The Harris Products Group has a product called Safety-Silv 56 with a 1200 degree melt temp. The description sounds exactly like the right thing for your application."

...RickJ6956, from http://www.doityourself.com/forum/electrical-ac-dc/121891-silver-solder-melt-temp.html#b

Chip

Tony Quiring · Sep 15, 2017

Using a Faber ware motor from a counter top cooker as they are readily available at yard sales and from factory as replacement part...and designed for this type of cooking.

Make bottom container to hold motor unmodified.

Shaft inserts into motor and protrudes from housing and top of housing is formed to cause anything dripped to drain to collection point but Bo seal at hole for now.

Shaft has male on both ends is critical.

A disk is made to cause drippings to land at edge of area away from possible entry into shaft hole but top of platform not allow uphill anyway.

Your spit that holds the meat is female so cleaning the interface is easy being easy wipe of machine and spit in sink.

No gears or chains to collect gunk and motor is an over the counter swap.

Forgot to mention bearings or other support may be needed above motor those are built into the housing and can be simple Teflon bushings due to slow speed

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

bigpaul22 · Sep 15, 2017

Thanks to everyone for the replies.

johansen said:
find a disk, epoxy/locktight/press fit it to the shaft so the grease is slung off the disk.

Is there a food-safe epoxy which can stand up to high temps?

jdavi581 said:
Need the bottom plate removable with the skewer-welded or pressed on so all the drippings are captured, basically a plate with a skewer sticking out. Take it out to wash, no way to get near the motor and easily cleaned. I would roll the edges up to make the plate, and pierce the center of the plate and TIG or spot weld to the skewer. To seal with the heat with the existing design, ceramic seals are likely to be the only thing to take the heat.
Joe

Yes this was my first idea too. Problem is I don't have a TIG welder, only a soldering iron or a brazing torch which is probably too big for the skewer.

Is there a method of applying ceramic seals I could do from home?

Chip Chester said:
Not much slingin' will be happening at 1 RPM.

Permanent solution is to mount the motor outboard of the cooking area, and use a chain drive like on baking/breading equipment. Stainless sprockets. Wipers on chain return to motor zone. Clean nightly, per NSF rules. (<--- that's the kicker.)

If you decide to solder, use silver solder. Lifted from a DIY site:

"Your basic silver solder has a melt temp of no more than 750 degrees or so.

Brazing, Soldering, Welding, Cutting & Gas Distribution | The Harris Products Group has a product called Safety-Silv 56 with a 1200 degree melt temp. The description sounds exactly like the right thing for your application."

...RickJ6956, from http://www.doityourself.com/forum/electrical-ac-dc/121891-silver-solder-melt-temp.html#b

Chip

The safety solder would be perfect although my current soldering iron only goes up to about 1000°F so I'll need to either find another safety solder with a lower melt temp, or try brazing using a blowtorch which might be too large for the fine skewer.

tnmgcarbide · Sep 15, 2017

yep, cheap as hell.... every yard sale and goodwill thrift store seems to have at least one. nobody uses them more than once or twice, or never at all..... they get filthy and rancid so you throw the thing away.

best bet= cover the thing with aluminum foil . the shade-pole motor shouldn't care .

bigpaul22 · Sep 15, 2017

(I posted a big reply but the mods must still be approving it!)

I use mine all the time. At least a few times a week, which is why I want to fix it permanently. Can't believe it's sent to market with such an obvious design flaw, though.

EDIT: It seems my reply isn't going to show anytime soon. To summarize, I basically said "thanks everyone", and I will go ahead with trying to fix the drip plate to the skewer permanently. I don't have a good enough soldering iron to solder pure silver solder and I only have a large brazing torch (too big) so I am going to try metal epoxy putty for the moment and see where that gets me. Thanks all.

johansen · Sep 15, 2017

Chip Chester said:
Not much slingin' will be happening at 1 RPM.

i know that.. but the grease will fall off the disk and build up on the motor, not drain down the shaft into the motor.

SAG 180 · Sep 15, 2017

Buy a stainless steel bowl or container like one of these and mount it on the spinning shaft using an aluminium flange for the shaft secured by a grubscrew. The container is upside down and spins on the shaft but acts as an umbrella for the motor.

208002d1505516546-looking-suggestions-how-grease-proof-synchronous-motor-food-use-set-5-pieces-stainless-steel-food-container-plastic-lid-onemegashoppe-1304-20-onemegashoppe_1_la.jpg

set-5-pieces-stainless-steel-food-container-plastic-lid-onemegashoppe-1304-20-OneMegashoppe_1_la.jpg

MrStretch · Sep 15, 2017

That contraption looks like a house fire.

DDoug · Sep 15, 2017

Chip Chester said:
Not much slingin' will be happening at 1 RPM.

More speed....More speed is always better.

I think 2800 rpm should be just about right..... :crazy:

Mike C. · Sep 16, 2017

O ring between the drip plate and skewer.

DDoug · Sep 16, 2017

MrStretch said:
That contraption looks like a house fire.

Heck, the gyro shop east of HGR has a gas fired one.....

Glug · Sep 16, 2017

Chip Chester said:
Not much slingin' will be happening at 1 RPM.

Well, then that settles it. You really need the low rpm torque of a DC motor with a good drive. And not a cheap one - those things cog. And if it cogs, it'll vibrate the juice out of your kabobs.

Contact Monarchist. I think he has a spare 10EE motor-generator setup.

There is nothing smoother.

DDoug · Sep 16, 2017

Instead of spending a bit more coin on a good one, spend hours modeling
the cheap one, posting pictures, write ups and strategizing.... :crazy:

Must be a tenured college prof...... :nutter:

MrStretch · Sep 16, 2017

I'm pretty sure that those rotating swarma/gyro things you see in restaurants are for keeping the pile of meat warm. They are cooked in separate ovens.

DDoug · Sep 16, 2017

MrStretch said:
I'm pretty sure that those rotating swarma/gyro things you see in restaurants are for keeping the pile of meat warm. They are cooked in separate ovens.

Yeah, I'm no fan of gyros, but always thought the meat was pan roasted, then
hung on that thing to give it a "Tan".

bigpaul22 · Sep 18, 2017

digger doug said:
Instead of spending a bit more coin on a good one, spend hours modeling
the cheap one, posting pictures, write ups and strategizing....

Must be a tenured college prof......

The modelling only took 20 minutes and was a lot of fun. I used "TinkerCAD" which is great.

The biggest problem is that there is no market for these devices for home use. So there is no "good one" I can buy, unless I spend thousands on a commercial-level one which I'm not ready to do yet.

MrStretch said:
I'm pretty sure that those rotating swarma/gyro things you see in restaurants are for keeping the pile of meat warm. They are cooked in separate ovens.

No, the meat is skewered raw and cooks only via radiant heat. The outside layer is continually cut off as it cooks. The assembled meat is usually used up quickly so there is no worry about bacteria etc., however it is generally considered safe to store any unused part of the meat overnight (in a refridgerator) for one night only.

Mike C. said:
O ring between the drip plate and skewer.

Yes, this was my first (and easiest) solution but I couldn't find a ring to match the diameter of the hole unfortunately.

In the end I have applied a small amount of JB Weld High Heat metal putty to permanently attach the drip plate to the skewer. The putty is food-safe according to their website.

I haven't tested it yet, but I'm confident it will be fine.

Thanks all.

Looking for suggestions on how to "grease proof" a synchronous motor (for food use)

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