View Full Version : ZAY7032G mill bearing temps

Your Old Dog
05-20-2010, 10:29 AM
I received an email from a fellow asking me for some actual temps. Here they are as they may help someone else with the same problem on the Harbor Freight Geared Head Mill/Drill known as ZAY7032G

Using a digital infrared themometer I came up with this.

Room ambient temperature 61 degrees

Mill ambient temperature as measured in the middle of the main housing and inches away from the thermometger was also 61 degrees and same with the bearing.

Cutting at 1500 rpm w/2flute 3/4" HS cutter taking about .040 depth in full width bite.

start Housing bearing

9:20 61 61
9:30 65.1 69.6
9:40 69.6 73.8
9:50 74.6 75.9
10:05 78.2 78.9
completion of job....

I just thought since the info was available it may as well be in the archives. Maybe someone will be helped by it.

05-20-2010, 03:15 PM
I have the same mill which I use as a drill press..I think it is the friction against the oil seal that heats the spindle up...It certainly gets warm quickly at high rpm's..

Your Old Dog
05-20-2010, 05:30 PM
I have the same mill which I use as a drill press..I think it is the friction against the oil seal that heats the spindle up...It certainly gets warm quickly at high rpm's..

I just got an email back from the guy who requested the information. That's what he wanted to know so you are helping him out. Anyone else notice that their spindle gets too hot on this machine. I'll send him another email and have him watch this thread.

I know this topic has come up before and that's the only reason I bothered with the post. I don't suppose Sir John and his band of merry "Bridgy" owners have to worry about this :D

05-20-2010, 07:31 PM
There are two things to consider:

1. How hot is "too hot?"

2. Is it stable, or does it just keep getting hotter and hotter?

#2 is the worst and indicates to much preload or perhaps bad bearings. Temp should stabilize relatively quickly and not keep climbing.

As far as #1, pretty darned hot is still not "too hot". 100 up to as much as 140 degrees F is fine. Fafnir even has a recommendation to run the spindle up to 150 degrees F, shut down, run it up again, rinse and repeat until it stabilizes at 130 degrees F as a break in procedure.

There's more data on spindle bearings on my page here:




Your Old Dog
05-20-2010, 08:37 PM
Here is what the gentle was actually asking me for when I answered the wrong question :D

His prime concern was the top of the spindle after the machine had been run for 5 minutes with the quill all the way down/extended and then put back up in home position.

Temperature at the top of the quill went from 71 degrees to 100 degrees in 7 minutes with quill all but fully extended (.250 withheld) In high speed mode of 1500 rpm and not under any load/cutting.

Now, the bearing housing has an inspection slot. When I put the IR thermometer up to the hole it reads the bottom of the spindle at 71.7 degrees. So allowing for a little error, one can conclude that all the heat is at the top of the spindle.

I did not lower the quill absolutely all the way because I never run my equipment at it's outer limits. I always raise or lower the head so as to have maybe 2 - 3" of Z at the most to reduce chance for friction. The only time I do lower the quill all the way is when I am tramming as I want to accentuate as much error as possible knowing it will get better as I lower the head.

Bob, thanks for chiming in.

05-20-2010, 09:44 PM
Did you use coolant or coolmist?

Heat from cutting travels up the tool into and out of the spindle to the quill housing.Just another factor to consider.

05-21-2010, 10:53 AM
I bought this gear head mill early in the year. After using it a while I found the ability to make a smooth (relative here) surface with a fly cutter difficult. Determined spindle bearings had play. Took spindle and bearings out. Found original Chinese bearings and decided to replace with new quality bearings. Went through the preload, run in, adjustment etc. The spindle bearings, both upper and lower DO NOT heat up and are not an issue. Sure they get warm maybe 10 degrees above ambient but are just fine.

During the course of replacing the bearings I happened to stick my hand up into the quill bore so that I could line up the quill for reinsertion into the head. This is when I discovered that the GEAR that drives the spindle was hot (a relative term but probably about 110 degrees by feel).

After the quill and spindle were replaced and the bearings were found to be fine I lowered the spindle and ran the mill for a few minutes at highest speed. When I raised the spindle to put some grease on it the spindle was TOO HOT to touch. I did further testing and with a thermocouple placed in the drawbar cavity found that the temperature was above 170F. I believe that the temperature stabilizes at less than 200F. This is with NO CUTTING LOAD.

This temperature rise is evidently being caused at the drivegear/spindle interface. The temperature rise is not as evident at low spindle speeds.

I want to know if this temperature rise at the spindle is experienced by others. I really don't want to take the head and gearbox apart if this temperature rise is "Normal".

The gearbox oil temperature gets warm to the touch (maybe 10 degrees above ambient) but that is a large mass of oil and metal and would take a long time to heat up if it were bad bearings on the drive gear. In addition if it was bad bearings I suspect I would be able hear them or other symptons would be present (such as noise and vibration). Maybe it is the oil seal but the contact surface for the seal should be very small and my initial thoughts are that a 200 degree temperature for seal friction is unlikely but I don't know for sure.

The mill was purchased new from Harbor Freight and I bought it used. I called Grizzly (they have a similar model) and asked their technician about the issue. Although they did the best to help they don't have an actual machine to run and test. In a nutshell, they don't know.

I hope I have been able to convey the issue to this group. Your help, ideas and comments are appreciated.

Arlington, Texas

05-21-2010, 12:51 PM
If the spindle is reaching 170F then so are the bearing races. That is well above the recommended maximum temperature. You do have a problem. For the gear drive to be causing that amount of temperature rise it would have to be howling too loud to stand. The likely culprit is either bearing preload, bearing misalignment or bearing race deformation when fitting.

I would remove the spindle and chuck it in the lathe to check for concentricity of the bearing seats and especially any out of round condition.

05-21-2010, 07:04 PM
I appreciate your comments - however during the run in and adjustment of the spindle the bearings did not get hot - the spindle above the top bearing gets hot quickly as does the drive gear. I will do as your suggest and check for concentricity.

Yes over time the spindle and bearings should reach an equilibrium temperature. According to the bearing manufacturer, SKF, 170 or 200F is not too hot for the roller bearings - I don't like them that hot therefore my concern.

The grease I used in the bearings is polyurea based and good for high temperature.



Don Young
05-21-2010, 09:43 PM
It may have nothing to do with the situation but high speed churning of grease or heavy oil creates a lot of heat.

05-22-2010, 06:56 AM
Perhaps the gear or its mate is not inline with the shaft, causing a rubbing motion as it rotates through its tooth contact?

05-22-2010, 07:36 AM
Well with mine it is the seal down the bottom causing the heat.... I took it for a run this afternoon at a high RPM and the spindle right at the bottom got too hot to touch within five minutes...

05-22-2010, 08:32 AM
I have the same mill which I use as a drill press..I think it is the friction against the oil seal that heats the spindle up...It certainly gets warm quickly at high rpm's..

About two years ago I did some rather extensive testing with common 6204 double sealed bearings from a variety of manufacturers. Some of the bearings I tested were SKF, Nachi, NTN and others.

The tests were part of a suitability study for operation at 10,000 RPM. One of the tests I performed was to remove the seals to determine how much of a temperature rise there was due to the seals.

In every case the temperature change was zero. If you think about it, if the seals were contributing to a temperature rise, they would melt.

In the end, it was determined that the allegation that seals contribute to significant temperature rise is a fallacy.

One of the other goals was to determine which bearings had the lowest temperature rise.

The winner was NTN. They consistently ran at about 140 degrees with all the others running at 170 or higher.

If you have a separate oil seal as I believe you have, it may be possible that the discrete oil seal is contributing to temperature rise. There is only one way to find out and that is to remove the seal and run it. I would be surprised if the seal was the culprit. I know if would be impossible to remove the seal and run it in that gear head mill.

05-22-2010, 04:21 PM
Were you using stock grease or a high grade synthetic designed for higher speeds?

As for tools heating up the spindle I have never had a tool holder holder even get warm with even something as light as mist coolant. Spindles heat up through their bearings. Thats why its a good idea to remove your tool after you are done for the day as the spindle can lock the tool in place. (Doubt this would happen on a R8 though)

05-26-2010, 06:53 PM

Thank you for your comments on my issue.

I removed the quill and spindle from the mill and ran the mill at high speed for about 30 seconds. I stuck my hand up into the quill cavity to touch the Quill drive gear. It was too hot to touch.


for an excellent picture gear configurations. The gears are actually attached to the top (the bottom of the picture) of the gear box.

From this experimenting I conclude the issue is not with the spindle, its bearings or anything related such as improper grease.

The quill drive gear is in an oil bath - I have to conclude that the oil seals have to be the friction generators unless the bearings associated with the quill drive gear are an issue. I still am not sure of anything because with this temperature I would have thought something would have failed by now.

Any additional thoughts?


Your Old Dog
05-26-2010, 08:48 PM
This link may show more:


05-26-2010, 09:28 PM
Additional thoughts:

Correct oil

Correct amount of oil

Switch to lower viscosity oil

Passive cooling and or active cooling of the head. Example:


05-26-2010, 10:49 PM
If your shafts aren't in line you'll get bad things happening. I mean, the bearings have to hold the shafts straight and not in a banana shape no matter how small.
I'd guess there's no way to reassemble the gearbox and check this, since the bearing bores are (presumably) in the bottom of the not shown bearbox,and in the top plate (shown in the pic).

05-27-2010, 04:47 AM
Well with mine it is the seal down the bottom causing the heat.... I took it for a run this afternoon at a high RPM and the spindle right at the bottom got too hot to touch within five minutes...

Well, I think you may just be being oversensative.
Humans start to cook around 50c, hardly a problem for anything metal.
2hp through a 90% efficent gearset is still 150~watts of heat disipated. Fair bit of heat if conduction away isent good enough.

I have heard of people even attaching an oil radiator (With or without fan) and pump to keep RF/IH gearheads cool at higher rpms.