MK VII control sheave bearing temp monitoring

[lahola1]

As most SS people know by now the weak link in the MK VII is the plastic speed adjusting cam melting caused by the control sheave bearing overheating/siezing up.
I think I have a fairly easy and inexpensive way to monitor the bearing temp while it's running.

Thru the back inspection cover hole I drilled and tapped a 6-32 hole in the side of the cam follower (pic 1).

Then I took a length of type K thermocouple wire; twisted the ends together.

I took a short 6-32 screw, flat washer and lock washer; screwed it in the threaded hole in the cam follower; put the bear end of the thermocouple wire under the screw and washer and locked it down.

Now with my type K digital pyrometer I can monitor the temp of the cam follower and bearing (my LCD display doesn't work too good anymore but I can still decypher reading)see pics.

I ran the ss for about 7-8 minutes; the temp went from 74 deg to 87 deg.

With this method you can monitor the temp as you work;find out what the normal operating temp is; and if it goes above that you know to lube or replace the bearing before catistrophic failier.

I found several thermocouple meters with a thermocouple wire for under $15.00 online.

I just set mine up for experimentation. If I wanted pretty it up I would drill a 3/16" hole in the back headstock cover to feed the thermocouple wire thru; leave some slack in the wire to allow control sheave movement and mount the monitor out front somewhere.

I hope my pics come across ok. I haven't tried this before.

[Dlawrencej]

that's a great idea I'm a new member to shopsmith I inherited a mark vii from my grandfather he bought new in 1964 and has taken very good care. I've completely gone thru and cleaned and serviced everything luckily my son in law is a machinist and when I came across that part and found it couldn't be replaced he made one exactly the same but in aluminum so far no problems just wanted to say your idea is great because your done if it melts.

[lahola1]

I started this thread a couple years ago now I got some projects going where I could get some time on my mk VII and get some temp numbers.
Nothing scientific, just temps over time.
Doing lathe work mostly steady with a few short stops; temps were about 107 deg in 30 minutes and about 115 deg in about 45 minutes.
Another day I was running the jointer mostly for about the same time and temps were about the same.
This is interesting info. I don't know what the max temp would be but it wouldn't be over 400 deg ( which is what it would have to be in order to melt the nylon plastic the cam is made of) unless the oil in the speed control bearing burnt off and seized up. I don't know, maybe the oil could burn off after running steady for 2 hours at medium speed.

I worked with thermocouples in the plastic industry for nearly 40 years. If you want more info on them, let me know.

[JPG]

Well that explains the yellow coil cord!

[StevenAyres]

This setup offers a good opportunity to do some science on this issue. Testing temps on the same operation before and after shaft lubrication, for example, could help confirm whether the problem is more with the plastic part or with poor lubrication.

I've done some temp-testing during operations on my VII using an infrared thermometer, and haven't seen anything like high enough temps to show risk of melting anything. That's not as reliable as the thermocouple, I expect.

How do you calibrate the thermocouple, by the way?

[JPG]

This setup offers a good opportunity to do some science on this issue. Testing temps on the same operation before and after shaft lubrication, for example, could help confirm whether the problem is more with the plastic part or with poor lubrication.

I've done some temp-testing during operations on my VII using an infrared thermometer, and haven't seen anything like high enough temps to show risk of melting anything. That's not as reliable as the thermocouple, I expect.

How do you calibrate the thermocouple, by the way?

One does not 'calibrate' a thermocouple. The thingie it is attached to maybe.

[reible]

Some where here I have some rolls of wire and some bricks with serial output, and maybe the floppy disks with dos software to log. I guess that is pretty much useless now. I also might still have a plug-in from Fluke to a multi-meter.... but almost as useless since the display on the meter fail years ago.

I have never seen a melted cam so if anyone has one it would be interesting to see just how it failed. I had thought there was a bearing like on the other shopsmiths that would fail and that would cause the cam issue, but I haven't felt the need to keep to much in touch with this issue since I don't have one to worry about.

Ed

[lahola1]

The main problem with an infrared gun is the smallest temp area it can see is about 1" diameter and the farther you are away from the subject, the bigger diameter it reads, so you are getting an average temp of all "things" it sees it that diameter.

Correct; you don't caliberate a thermocouple wire. It is just a length of two dissimmilar metal wires sending a millivolt signal to a pyrometer that converts that signal to a temp (F or C) that we can easily understand. A type J thermocouple is Iron and constentan. Pyrometers are set at the factory and generally aren't changed unless your manual tells you how.
You can check it with a bowl of ice water and boiling water ( adjust for altitude) to confirm it is fairly accurate.

Plastic cam; this is the only pic I have of a damaged plastic cam. It is so damaged it's hard to tell if it is melted or smashed. I think it melted from a seized bearing and someone tried force it with the speed control in its melted state.

StevenAyres; I may do some more accurate testing in the future. I think for now I feel safe to lube regularly, in vertical position to be sure the oil soaks into the bearing and let it rest for a while after running an hour. I wouldn't run it over an hour unless I was temp testing.

[redleg]

Here is a Mark VII cam from a unit I bought for parts a few years ago. The bearing had overheated and melted the cam in several spots. I filled the voids with hot glue to use it as a pattern.

IMG_0419.JPG (62.55 KiB) Viewed 8132 times