L&R Cleaning Machines

[watchweasol]

It does look a bit rustic, may be better after a good clean and a good dose of looking at. Usually wire wound pots are pretty hardy unless some butcher has bbeen at it.  Clean it up then re assess. 

[SonnyBurnett]

8 hours ago, Plato said:

No way I'd reuse that part, it's already been mucked about with, replace it with a new pot. I bet the knob is a standard size used today.

https://uk.rs-online.com/web/c/passive-components/variable-resistors/potentiometers/?searchTerm=potentiometer

that was my first thought.  "This has been messed with" but it's old and this is my first machine, I thought it could have just been a bit crude.                                                                                                                                                      I kind of want to replace it too.  Problem is like with your link you sent me, I don't know what replacement part I actually need.  I talked to Dave at Dave's Watch Parts and said he used to buy them at www.surplussales.com, but I still don't know exactly what to get.  115 volt at 75 cycles and I think it's 60 Ohm.

Edited November 25, 2021 by SonnyBurnett

[Plato]

23 minutes ago, SonnyBurnett said:

that was my first thought.  "This has been messed with" but it's old and this is my first machine, I thought it could have just been a bit crude.                                                                                                                                                      I kind of want to replace it too.  Problem is like with your link you sent me, I don't know what replacement part I actually need.  I talked to Dave at Dave's Watch Parts and said he used to buy them at www.surplussales.com, but I still don't know exactly what to get.  115 volt at 75 cycles and I think it's 60 Ohm.

I don't suppose you can find a circuit diagram? I sent the wrong link too, this is the correct link:

https://uk.rs-online.com/web/c/passive-components/variable-resistors/rheostats/

There must be something equivalent to what you need. But, like others have said, it might look/work a lot better when cleaned. 

[SonnyBurnett]

I'll try to clean it up.  I'd feel better replacing though if someone can find me an exact replacement, by which I mean one that will work, it doesn't have to be exact or NOS.

[SonnyBurnett]

Dave contacted me and said this one might work.  Anyone got any thoughts?  Its on the very bottom of the page.

(RWA) A-29418-5

  https://www.surplussales.com//Potentiometers/Rheostats/PotsRheost-3.html.

[Plato]

9 hours ago, SonnyBurnett said:

Dave contacted me and said this one might work.  Anyone got any thoughts?  Its on the very bottom of the page.

(RWA) A-29418-5

  https://www.surplussales.com//Potentiometers/Rheostats/PotsRheost-3.html.

Do you mean the (RWA) RP151SD750KK? I can't find (RWA) A-29418-5.

75ohm would be near enough to 60ohm for a rheostat provided it can cope with the current/power.

[SonnyBurnett]

14 hours ago, Plato said:

Do you mean the (RWA) RP151SD750KK? I can't find (RWA) A-29418-5.

75ohm would be near enough to 60ohm for a rheostat provided it can cope with the current/power.

At the very bottom of the page in the link on the right side.  The last one.  On my screen it shows up as (RWA) A-29418-5

Rheostat, 800 ohm, 50 watt, 0.25 amp. Type R-50. 2-1/4" diameter body, 1-3/8" behind panel depth. 1/4" diameter x 1/2" long round shaft. Made by Memcor. NSN: 5905-01-013-4370.

Dave said this one is close enough it should work.  One thing I noticed is the wattage.  it's 50 watt and the machines are rated at 60.  Also the amperage, seems low.  Can't remember what the machine runs at.

Edited November 27, 2021 by SonnyBurnett

[Plato]

10 hours ago, SonnyBurnett said:

At the very bottom of the page in the link on the right side.  The last one.  On my screen it shows up as (RWA) A-29418-5

Rheostat, 800 ohm, 50 watt, 0.25 amp. Type R-50. 2-1/4" diameter body, 1-3/8" behind panel depth. 1/4" diameter x 1/2" long round shaft. Made by Memcor. NSN: 5905-01-013-4370.

Dave said this one is close enough it should work.  One thing I noticed is the wattage.  it's 50 watt and the machines are rated at 60.  Also the amperage, seems low.  Can't remember what the machine runs at.

Is this is the circuit diagram to your machine?

What motor does it use? We could figure out the current.

[Plato]

Maybe the '(RWA) 2286013-1' would be better at 50ohm. The shaft for the knob is the same and it has a higher current rating.

https://www.surplussales.com/Potentiometers/Rheostats/PotsRheost-2.html

[HectorLooi]

A new rheostat would be quite costly, probably about $150. Another alternative to consider is to completely modify the circuit and use a SCR controlled ac motor controller. A ready built board can be purchased from a number of online sellers for less than $5.

[SonnyBurnett]

7 hours ago, Plato said:

Is this is the circuit diagram to your machine?

What motor does it use? We could figure out the current.

Yes that's it.

[LittleWatchShop]

How come you do not measure the rheostat in place?

[Plato]

21 minutes ago, LittleWatchShop said:

How come you do not measure the rheostat in place?

I think he did, 60ohms.

One thing I read about earlier was that some of these old rheostats might use asbestos as insulators, another reason to replace it. 

[jdm]

15 minutes ago, Plato said:

One thing I read about earlier was that some of these old rheostats might use asbestos as insulators, another reason to replace it. 

Why. That would be another case of unjustified fears of a danger that scientifically doesn't exist when exposure to the harmful substance non-existent, as when asbestos is firs and solid, and in a minuscole amount. One needs years of continuous exposition to fibers to get in danger of developing lung cancer.

[LittleWatchShop]

49 minutes ago, Plato said:

I think he did, 60ohms.

One thing I read about earlier was that some of these old rheostats might use asbestos as insulators, another reason to replace it. 

60 seems low to me.

[Plato]

2 hours ago, jdm said:

Why. That would be another case of unjustified fears of a danger that scientifically doesn't exist when exposure to the harmful substance non-existent, as when asbestos is firs and solid, and in a minuscole amount. One needs years of continuous exposition to fibers to get in danger of developing lung cancer.

@jdm what part of the world do you live in that you don't consider asbestos a risk?! 

[Plato]

2 hours ago, LittleWatchShop said:

60 seems low to me.

Have a look at the schematic. Aren't you a PhD in electronics? 

[LittleWatchShop]

4 hours ago, Plato said:

Have a look at the schematic. Aren't you a PhD in electronics? 

Your hand drawn schematic is wrong at least in one place.  Furthermore, I measure the rheostat on my cleaning machine and it measures closer to 800 ohms.  And, yes, I do have a Ph.D. in electrical engineering.

[LittleWatchShop]

[HectorLooi]

Even a PhD won't be able to tell the correct value for the rheostat with the limited information given. 

The value would depend on the internal resistance of the motor used in the machine. I'm sure the motor must have changed over the decades of production.

But 50 ohms does seem a little low.

[Plato]

7 hours ago, LittleWatchShop said:

Your hand drawn schematic is wrong at least in one place.  Furthermore, I measure the rheostat on my cleaning machine and it measures closer to 800 ohms.  And, yes, I do have a Ph.D. in electrical engineering.

It's not my diagram, I found it on the nawcc website. 

[Plato]

6 hours ago, HectorLooi said:

Even a PhD won't be able to tell the correct value for the rheostat with the limited information given. 

The value would depend on the internal resistance of the motor used in the machine. I'm sure the motor must have changed over the decades of production.

But 50 ohms does seem a little low.

I did ask about the motor. 

[jdm]

11 hours ago, Plato said:

@jdm what part of the world do you live in that you don't consider asbestos a risk?! 

In one where science is taught. I never said asbestos is not risky, but that it is in certain quantities and modes.
Fearing otherwise is unwarranted paranoia. Quote fron the first article I rant into:

A one-off exposure from do-it-yourself renovation is not a major risk
https://www.asbestos.com/exposure/short-term/

There is a major difference between asbestos in tons, or fractions of, and the scarce gram which could a sigle electronic insulator. Beside, isn't even proven than what is being discusses is indeed made of that.

[jdm]

6 hours ago, HectorLooi said:

Even a PhD won't be able to tell the correct value for the rheostat with the limited information given. 

Maybe a PhD doesn't, but people of practical experience do. As mentioned, 50 or 60 Ohm is little for any "power application".

[Plato]

7 hours ago, LittleWatchShop said:

What was stopping from sharing this information with @SonnyBurnett when he first asked? Is it more important to try and prove someone wrong rather than to help another out?