Open or Sealed Bearings?

      A shop owner struggles with a decision about after-market bearings for an older Italian moulder. March 4, 2009

Question
Im looking for some guidance on bearings. I have an older Sicar moulder in need of some new bearings on a head. I have been unable to find the US parts/distribution for Sicar, and the Italian site is under construction, so I'm somewhat left to my own devices here. If anyone knows of parts/service stateside and wants to share, that would be great.

The machine is 230X160 capacity, 40mm shaft, 6000 RPM, 7 head with outboard bearings. The spindle bearings are in 2-1 configuration, double 6010's at the working end, and a single 6208 at the back/pulley.

I've used sealed SKF's in the past and had good luck (I think), but am wondering if they are appropriate. After discussing with my bearing supplier, I've been using an ABEC 1/ISO Normal bearing. Talking with my tooling supplier, it sounds like I need to use a better bearing, but I don't know how far to go.

ABEC 3/ISO P6 or ABEC 7/ISO P4 are both available, but drastically different. The P6's are a sealed bearing similar to what I've been using with better tolerances, but the P4's are a open bearing in a phenolic raceway, and better tolerances than the P6's. I'm hesitant to go this route due to decent, not great, dust shield/guard on the shaft system itself.

There is also a solid lubricant available that might make sense rather than grease, but I don't know. Again tooling supplier recommended a specific grease that was too much money a quart, which leads me to think open bearings are common, but may not be practical for my machine.

The basic question is: can someone(s) answer what grade/type bearing is typically used on a moulder spindle, or knowing there are dozens of answers to that, what might be recommended? Also take into consideration that the machine is older, and as such I don't know that current tolerances are possible, or were even when new- things have changed since 1989.

To answer some questions/comments that I'm sure some might be wondering, the complete spindle is off the machine and bearing work is done on a press, with heat/cold as necessary. The spindle then is checked with a dial indicator with the assembly clamped to a granite surface plate. I leave the sledge hammer in the truck, and try to be as careful as possible knowing the tolerances that required/desired. Any help would be greatly appreciated, thanks in advance.

Forum Responses
(Solid Wood Machining Forum)
From contributor D:
Only use the unsealed bearing if the spindle assembly has sealing capabilities. If you have good luck with the one rating and you go to a higher rated bearing you should be alright. In most cases a high end bearing such as SKF's precision grade bearings are better than most OEM bearings.



From Dave Rankin, forum technical advisor:
I would recommend the following:
1. If you have ability to grease the spindle bearings after assembly, then an open bearing is what I use. If there are no grease fittings, then either type of bearing will work.

2. Only half pack the bearing, otherwise you will overheat the bearing as it is run in.

3. The higher the grade of bearing, the better accuracy you will have; however, you can spend a lot of extra money and not gain anything on your machine. I run an older Weinig moulder with both high precision and standard bearings. I replace the bearings with what the spindle is rated for. Better bearings "may" show a better rotation if the spindle parts are made to the higher accuracy. On many machines, the accuracy of the spindle parts will reduce the affect that higher accuracy bearings will have.

4. If you are having good results with the process that you have followed, I would continue this process. If the results are not what you would like to have then try a spindle with upgraded bearings. Be aware, that having only one spindle with upgraded bearings and the rest with standard bearings, may or may not show any real change. Each spindle on a moulder affects the finish of the entire machine.



From the original questioner:
Dave - thank you for the response. I cannot grease the bearings after assembly, so I am going to continue to use sealed bearings, but am I'm going to try the P6's, only about twice the price or $40 as what I've been using, as opposed to $180 for the P4's which I couldn't use anyway.

I understand completely about paying lots of money for no noticeable gain. My question is to try and get a baseline to work from/compare to on my machine. The manual I have leaves a bit to be desired - even if I could read Italian, there are only three pages of text in it, the rest are parts diagrams. So I have nothing to start from, other than what I glean from this site and talking with other owners/operators. I'm trying to get as close to original as I can, to flush out any remaining demons from its previous use.

I understand that one change may make no discernable difference by itself. However, I don't mind spending a few extra dollars for the peace of mind that I've done what I can.



From the original questioner:
A follow up for those interested. With a new set of "regular" bearings in, I measured .0005" TRI at the housing end, and .0007" TRI at the outboard end of the shaft. Pulling those and putting in the P6 "precision" bearings, I now have .0002" TRI at the housing end, and .0004" TRI at the outboard end. So the bearings halved my run-out on a surface plate. But after reading the "Welded Head to Spindle" thread, I'm concerned I have further problems.

According to what was posted in that thread, run-out should be measured in microns, or .000001". A run-out discrepancy of more than .00002" with new bearings may indicate a shaft problem.

Given the age of my machine, and the years of use, I doubt I can ever get to that kind of accuracy, short of replacing the shafts, which is not out of the question, but obviously would like to be avoided for hassle and expense.

Does anyone have any thoughts or comments regarding this information/situation? Do I need to look at replacing the shaft or am I just going to be chasing my tail so to speak?



From contributor R:
Previously I mentioned 15 microns bearing change (.0005") roughly, 20 microns maybe shaft change .0008" roughly. So if you have changed the bearings and got .0002" and .0004" run-out, I would say you have successfully changed the bearing and got within mfg specs.


From the original questioner:
To contributor R: thanks for the explanation. I got myself confused with regards to microns. I forgot to do some converting from metric I think.



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