[promehanik]

I am prepairing for build spindle for small grinding machine. Axial forces will be in both directions. I found this drawing. I would like remove tube which is between inner rings. This get me possibility for change bearing preload (ball bearing with angular contact) during the use. Is this acceptable? Maybe this tube have any influence on rigidity of spindle?

regards,
Promehanik

[RICHARD ZASTROW]

That tube or spacer controls the preload of the angular contact bearings. It also contributes to the rigidity of the spindle assembly.

Dick Z

[mactec54]

promehanik

The tube is needed as it is part of the preload in this design, but the length does not have to be precise as you have the springs which give you the preload ajustment required for these bearings, for a grinding spindle you want a flat belt or a poly-v belt type not the deep vee pully in this design

[promehanik]

I developed new design of spindle for 2 wheel grinding machine. On each end of spindle will be diamond grinding wheel (diameter 200 mm). Please tell me if bearing arrangement is suitable. Inside diameter of bearings is 50 mm.

regards,
promehanik

[RICHARD ZASTROW]

The bearing arrangement seems OK. I'm assuming the bearings are sealed type or there are seals in the final design.

The end with the pulley and a grinding wheel might need an additional bearing to compensate for the heavier radial load.

Dick Z

[promehanik]

In the final design will be seals.

The end with the pulley and a grinding wheel might need an additional bearing to compensate for the heavier radial load.

Maybe is better, that I move pulley on other end of shaft (near the 2 preloaded bearings)?

regards,
promehanik

[promehanik]

I prepeared new design. What do you think abou it?
I want wery precise rotation.

regards,
promehanik

[RICHARD ZASTROW]

promehanic, If all your bearing life etc. calculations are correct, it should work OK.

Remember, high precision work requires high precision bearings. The higher the precision, the higher the price $$$$$$$$$$$$$$$$$$.

Dick Z

[promehanik]

I do not want use matched bearings, because of price (very expensive).
- Please tell me if is possible matched bearings at home?
- Please suggest me any other bearings and arrangement?

On both sides I want precise rotation.

Regards, prom

[RICHARD ZASTROW]

promehanic, You will have to be more specific.

What speed do you intend the spindle to operate?, What is the maximum run out (tir)? What is the radial load? What is the axial load?

What one person thinks is precise may be different than mine or yours.

Keep working at it.

Dick Z

[promehanik]

speed: 3000 rev./min
run out: 0,03 mm
axial force: 200 N
radial force: 200 N

regards, prom

[RICHARD ZASTROW]

prom, next question; what ID @ OD etc. are the bearing dimension requirements?

Dick Z

[promehanik]

Inside diameter: 45 mm
Outside dia.: 100 mm

regards, prom

[wildwestpat]

Hi Prom

The speed - run out - shaft loadings - cost sensitivity requirements you have stated all point to a much simpler solution using taper roller bearings. Branded 45 x 100 x 27.3 can be had for £25 in the UK which is half the price budget AC types. Taper roller races are relatively insensitive to pre-load and this simplifies the construction. If you are content with 3000rpm then you don't need the complications of angular contact bearings. Suggest you look at the data sheets from the various bearing makers as well as what is available locally from bearing stockists. The common sizes are a lot cheaper than the less frequently used types.

Hope this saves you cash as well as machining time.

Regards

Pat

[RICHARD ZASTROW]

Pat is correct in that tapered roller bearings are less expensive and require less machining.

High precision tapered roller bearings are also expensive. Check the bearing tolerances and compare them to your requirements. Also, consider your lubrication and sealing requirements.

Angular contact bearings, even the highest precision, can be purchased with lubrication for life as well as sealed. Many, if not most, commercial spindles are constructed this way.

Dick Z

add; .03mm (.0012") tir is not all that critical/precise. You won't require either high grade A/C or tapered roller bearings.

[wildwestpat]

Hi Prome

Also you need to think about the cutting loads and the robustness of the spindle. The spindles in most lathes and milling machines use taper roller bearings as these give good spindle support (ridgidity) and a good margin for both axial and radial forces generated during machine use as well as a margin for the inevitable abuse! To get similar axial and radial load factors from angular contact bearings you would have to use multiple bearings and these are very difficult to mount and use correctly so that the load is shared between the bearings.

You may even find that normal deep grove ball bearings will give you the required axial support as the speed and run out you have specified are easily obtained with the less exotic types of support bearings.

It would help a lot if you were to post the cutter types, materials and feed rates you are proposing to use this spindle with. Also the proposed tooling holder as some require a lot of force to change the cutting tool which in some cases is applied via the spindle bearings. Are you considering the extra forces applied when or if the tool digs in? Don't ask me why I think this is important but I do have a fine selection of tool bits minus their cutting faces! Also don't ask me how much extra force is necessary as I use a fudge of ten times the indicated cutting force and to date this has been adequate.

Also SKF have a very good (simple) bearing selector on their web site which may help you select the most appropriate bearing for your application. However do keep in mind what is obtainable locally from vendors stock. Ignoring the fancy tight tolerance bearings there are basically three categories - unbranded & sold lose - unbranded sealed packages - branded boxed and sealed packages. For a spindle I would opt for the branded boxed bearings from one of the well known manufacturers as the premium is small and the quality is known from the spec sheet.

Hope this helps you get going and just don't forget use common sizes where ever possible unless you have a compelling reason to use the exotics!

Regards

Pat

Hope this helps

[RICHARD ZASTROW]

prom, Pat is again correct. There are lathes and mills that use tapered roller bearings. In fact, I replaced them in a gear hobbing machine @ $16,000 for the pair. (Precision bearings are expensive).

Bridgeport mills use special angular contact bearings. Again, expensive.

The tapered roller bearings used in good quality lathes and mills are precision bearings, and are quite expensive, not the cheaper general purpose type.

For your small grinding spindle, standard taper roller bearings will probably suffice. They will withstand more radial force as well. You will have more radial force on the pulley side due to belt tension.

The spindle ends will still need sealing.

Pat is also correct about possibly using ball bearings. If you order brand name sealed deep groove bearings with C2 (less than normal) clearance, you should be able to absorb the relatively light axial load. The clearance for a 45 mm bore deep groove C2 bearing is 1 micron min., 11 micron max.

Check the bearings catalog specifications to assure you are meeting you load and speed requirements. The higher the class of bearing, the more $$$$$$$$$$.

Do not forget to have excess capacity. (fudge factor)

Dick Z

[RICHARD ZASTROW]

I read the thread over again. I missed the point of this being a spindle for diamond grinding.

Can you describe the purpose of the grinder? Is it a peripheral (grind on the OD of the wheel) or a flat grinder (end/face of the wheel) like a disc grinder?

Dick Z

[wildwestpat]

Hi Prome

Good for Dick Z in looking back to your first post. I do not think you should be mounting large grinding wheels using what I take to be a jacobs taper as used for drill chucks. Any vibration could easily cause the wheel to come off and 3000 rpm will cause it to travel arround your work space in an alarming way.

Think about using a threaded retaining nuts with left and right handed threads so that the rotation of the spindle causes the nuts to tighten. Use a precision register diameter and shoulder to ensure the diamod disk is properly centered and runs true each time it is mounted. If you intend to use diamond wheels that have a resin bonded rim of diamond compound then these have an alloy core that has a precision bore and a machined face on which the wheel can register to run true.

Hope this helps

Pat