EQ6 bearing upgrade

[Starflyer]

Hi all,

I've taken the plunge and decided to strip and tune my EQ6 Pro over the summer. I've already ordered the ceramic 608 worm bearings and PTFE worm wheel spacers from astro rubylith across the pond, and I've ordered the SKF thrust bearings from a UK source.

I'm struggling to find a source of the SKF 6008 2RSJEM bearings that George recommends in this post, but have found plenty of other 6008 bearings available online. Are any of the 6008s from this page suitable and is there any benefit in replacing the full set of 6 over just the 2 that most re-build articles suggest you change? I'd like to stick with SKF or another decent manufacturer.

Cheers,

Ian

[wayne weedon]

Hi

Not sure what the JEM in that number refers to. But 2RS just means two rubber seals. 6008 is a stock bearing. Other common bearing designations are ZZ which means 2 x metal Shields, where Z means one.

Why did you go for Ceramic bearings? Normally their use is for high speed applications like turbines and some machine spindles.

If you want accuracy opt for the highest ABEC number you can afford. This additional designation covers aspects such as Radial Runout.

Wayne....

[Starflyer]

Hi Wayne,

Thanks for the reply and advice. I went for those bearings as they're commonly mentioned in EQ6 tuning sites and threads and I wanted to get the worm wheel spacing washers from them at the same time.

The main problem I have is sporadic tracking errors up to about +/- 10 arc seconds when imaging and guiding at longer focal lengths. The periodic errors are manageable and I can mostly guide them out very accurately. I have a feeling there's some swarf or paint flakes in there causing the random errors and I always planed to change the bearings (including the thrust bearings) for a known brand while it was apart.

I'll hopefully make a start on it tomorrow evening and I'll report my findings.

Thanks again,

Ian

[ponytale]

foound this text on bearing web site regarding JEM designation, hope it helps ...Radial internal clearance (table 1)

SKF single row deep groove ball bearings

are produced with Normal radial internal

clearance (CN or C0 not marked on

bearing) as standard. Radial clearance

selection is based on factors such as high

speed, operating temperature, shaft fits and

axial movement limitations. The availability

of bearings with clearances other than

Normal should be checked before ordering.

The suffix JEM indicates an internal

clearance greater than Normal (C3). Many

of the bearings, particularly the smaller

sizes, are also available with radial internal

clearance, which is greater than or less

than Normal (C3, C2 respectively).

The values of the clearance limits for single

row deep groove ball bearings are shown in

table 1. They conform to ISO 5753-1991

(ABMA standard 20-1996) for the size

range covered by this standard. The values

apply to unmounted bearings under zero

measuring load.

Deep groove ball bearings

[wayne weedon]

Thanks for looking that up.

BUT. You should be careful with Radial Clearances on bearings. I am very familar with the C3 types. These are used a lot in the motorcycle engines which part of my business is based around.

Increased radial clearances are normally used where a bearing has to live in a higher temperature enviroment ie Engine Main Bearings. To avoid the bearing spinning in it's housing as the crankcases expand a tigher bearing fit is used. These bearings have to have increased radial clearances otherwise they would bind in the tighter than normal bearing housing.

So unless the housing is designed for tighter bearing fit the bearing would effectively be running with sloppy internal radial clearances.

Wayne.....

[wayne weedon]

I googled it "JEM" a moment ago and came up with some stuff from a legal case notes.

"It came to light during the hearings held at the USITC in Washington DC that SKF USA sold numerous bearings that were not designated JEM for electric motor use. The JEM designation signifies two things: a C3 fit and polyurea grease. The EM stands for electric motor. According to SKF USA, they do not authorize the sale of non-JEM bearings for electric motor use in the United States."

So basically it seems "JEM" are a C3 fit bearing with a particular grease for electric motor use.

Wayne....

[Starflyer]

Interesting info, many thanks.

I went for standard clearance SKF RS2 bearings in the end. The Dec axis is stripped down, there's signs of ground up paint in the grease on the worm and wheel and I've found a few very small bits of steel swarf too. The worm housing mating faces have a liberal amount of paint overspray on both of them, the next job is to clean these up in preparation for the reassembly.

The Dec thrust bearing also felt slightly rough when I was turning it by hand without the Dec shaft fitted. I'm replacing both of the thrust bearings anyway, but I'll clean the old ones up and have closer a look at the surfaces.