Thread: Tool Post Grinders - Can A good one be made?

This was marked on the box my replacements came in. FAG / Barden Aerospace 200HC B7200C.T.P4S.UL. Good for 85,000 RPM with oil lubrication . See page 25 in this link.

- http://www.bscindia.com/catalogue/FAGPrecBrgsCat.pdf

The need for speed comes at a price though!

BT

Simon.

I rang one of my bearing suppliers. I've found a pair of Fafnir 2MM200W1DUL. Same / same only a different number. $102 for the pair.

Ex stock Melbourne.

Regards Phil.

Hi Phil Hi Bob, Thanks for your input and advice. I ended up getting a reply from the seller of that bearing on ebay. He confirms that it is definitely an FAG B7200C.T.P4S.UL (similar to yours Bob except yours has ceramic balls I think) and states that its old new stock from a customer that went broke. One only though and if I want anymore they will be $165 each. Not sure if I did the right thing but I bought it, that was before I saw Phils offer of $102 for a pair! That's a bloody good deal. I have searched the web high and low and the best price I could find was about $100 each + delivery. Phil, if this bearing turns out to be legitimate, can you buy them single or am I now stuck with a spare? Yes, I am a tight wad! Cheers, Simon

Originally Posted by simonl

The trimmer runs at 30K which in some ways presents some challenges. It means I cannot change speeds purely electronically if I want useable operating speeds from 6,000 to 38500 rpm.
Cheers,

Simon

Hi Simon. Why are you looking to drive the TPG spindle to 38,500 RPM?

I have a C0 Waldown TPG, and as the safe surface speed of a bonded grind stone is approximately 32 metres/second, that equates to a quill speed of 24,000 RPM for a 19 mm internal abrasive.

So 24K is a hard as you will ever need to drive it - for small diameter stones.

Incidentally, the Waldown uses hi speed magneto bearings (open cage ball race) in both quills.

I had to replace one and bought a full set for both quills - $25 each from CBC Bearings.

Rob

Originally Posted by nearnexus

Hi Simon. Why are you looking to drive the TPG spindle to 38,500 RPM?

I have a C0 Waldown TPG, and as the safe surface speed of a bonded grind stone is approximately 32 metres/second, that equates to a quill speed of 24,000 RPM for a 19 mm internal abrasive.

So 24K is a hard as you will ever need to drive it - for small diameter stones.

Incidentally, the Waldown uses hi speed magneto bearings (open cage ball race) in both quills.

I had to replace one and bought a full set for both quills - $25 each from CBC Bearings.

Rob

Hi Rob,

That's a fair point. I have never really used a TP grinder for internal grinding. I just had the idea of returning the dumore back to it's original capacity, which is running a 1/8" grinding wheel at 38K. Will I ever need to internally grind a bore that size? probably not but hey why not have the option! I dare say any future use of this unit will be mostly external grinding needing little more than maybe 6000 rpm.

How come you can get $25 bearings for your grinder?

BTW, I did some more testing of the spindle with a 2um dti. It tells a different story. The runout seems to be about 0.01mm but totally random in location (high spot changes from one turn to the next). I dare say this points to the bearings being shagged afterall.

Simon

Originally Posted by simonl

Hi Rob,

That's a fair point. I have never really used a TP grinder for internal grinding. I just had the idea of returning the dumore back to it's original capacity, which is running a 1/8" grinding wheel at 38K.

How come you can get $25 bearings for your grinder?

Simon

I wondered if you were trying to run diamond burrs in it - that's the only reason for such a speed.

I get my bearings cheap because I am cheap. He he. No not really. These are a standard high quality magneto bearing (NSK) and don't cost an arm and a leg.

My TPG doesn't have a collet chuck, and can't drive burrs. But then again, I can't see when I would ever need to do that.

Your bearing runout could also be due to incorrect adjustment.

Rob

Originally Posted by nearnexus

I wondered if you were trying to run diamond burrs in it - that's the only reason for such a speed.

Rob

Hell no nothing like that. My machining requirements (and skills) are fairly basic compared to many on here. I seem to be consistantly 3-4 years behind everyone else on here. What's new to me, has usually been discussed here some years back.

Simon

Simon,

Can you check the trueness of the spindle between centres? I never looked at the condition of its centre holes and if they are knackered I don't know how they could be made good enough to provide the accuracy required for checking runout. It would be pointless throwing money at any bearings if the spindle is bent.

I do agree, Rob's NSKs are appealing. The internal grinding spindle on the Hercus No. 1 does not have hundred dollar bearings fitted neither does the main spindle.

Apart from the grit, my other issue with the Dumore was motor vibration. Having bought the thing second hand and never experiencing the live working of a new Dumore, it's hard to know what is normal. Alan "C-47" has a Waldown ( a CO I think ). It too vibrated but to a lesser extent than my 44.

If I did have reason to use a grinder on the lathe and let's say it was the Dumore I'd be tempted to ditch the motor and rig up an external drive along the lines of Schaublin's. Whilst the photos show a milling spindle, the grinding spindle setup is the same.

BT

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Originally Posted by Anorak Bob

Simon,


Apart from the grit, my other issue with the Dumore was motor vibration. Having bought the thing second hand and never experiencing the live working of a new Dumore, it's hard to know what is normal. Alan "C-47" has a Waldown ( a CO I think ). It too vibrated but to a lesser extent than my 44.

BT

I don't have any motor vibration issues at all with my C0 Waldown. It's many years old, but absolutely silky smooth.

The motor does scream very loudly, but the bearings are all good and lubed - just the nature of the beast.

The only issue I have is that the internal quill spits oil at me (severely) at the drive belt end.

I made up a replacement felt seal for it after the last time I used it (recently to true my scroll chuck jaws), cause I looked like Mel Gibson from Braveheart after with half my face and neck white and the other half black with oil. Had to use copious quantities of hand degreaser to get it off. Not the first time it's got me.

I haven't tested ithe new seal's effectiveness yet.

Interestingly, I don't see these felt seals in the Brobo spares listing, so I guess they are made from unobtainium. However, very simple to make with a couple of knock up wad punches.

These grinders are great for restoring chucks - my 10 year old old Chinese scroll chuck internal jaws came back to 0.02 - 0.025mm repeatable across a wide range of work sizes after this treatment.

Very handy item.

Rob

Originally Posted by nearnexus

These grinders are great for restoring chucks - my 10 year old old Chinese scroll chuck internal jaws came back to 0.02 - 0.025mm repeatable across a wide range of work sizes after this treatment.

Very handy item.

Rob

I think I saw that on your you tube channel.

Simon

Originally Posted by Anorak Bob

Simon,

Can you check the trueness of the spindle between centres? I never looked at the condition of its centre holes and if they are knackered I don't know how they could be made good enough to provide the accuracy required for checking runout. It would be pointless throwing money at any bearings if the spindle is bent.

I do agree, Rob's NSKs are appealing. The internal grinding spindle on the Hercus No. 1 does not have hundred dollar bearings fitted neither does the main spindle.

Apart from the grit, my other issue with the Dumore was motor vibration. Having bought the thing second hand and never experiencing the live working of a new Dumore, it's hard to know what is normal. Alan "C-47" has a Waldown ( a CO I think ). It too vibrated but to a lesser extent than my 44.

If I did have reason to use a grinder on the lathe and let's say it was the Dumore I'd be tempted to ditch the motor and rig up an external drive along the lines of Schaublin's. Whilst the photos show a milling spindle, the grinding spindle setup is the same.

BT

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Hi Bob,
Testing B/T centres had crossed my mind but I'm yet to do it. Not sure how reliable the centre holes are but worth a try. Other option is to rest the bearing journals on V blocks and check that way. Work prevents me from anything right now but will attempt to get a final picture of the spindle on the weekend.

Remotely mounting the motor looks bloody complicated for something that may only get used 3 -4 times a year. There is a strong case for a cylindrical grinder isn't there?
Simon

Morning all,

bit of a rush this morning but I had a look at the runout with the spindle bearing mounts resting on V blocks. Runout is around 5um so about 2 tenths. I'm happy with that and happy to go ahead with the project. Didn't bother to use the centres as they look a bit shabby.

Simon

Hi Simon,
When i crown wheels i set the compound to 1 deg and taper the wheel off each edge for about 2/5 of the width. Then you can blend the flat spot with a file/emery. 1 deg gives you about the 1/8" per foot, without measuring i think thats what my waldown would have. It has ally wheels but they are very light, with only a thin face and web connecting to the hub for the larger ones, i think the little (25mm) one is solid.

I have wondered if a water cooled cartridge spindle might be the way to go, but then even the cheap ones are not that cheap!

Thanks Ueee,

crowning the wheels has had me stumped. I was wondering whether a ramp up and down from the centre would "do the job" Using emery to "blend in" the ramp in the middle may just be the go. I was also thinking of cheating and just doing a flat pulley with 2-3mm lip on each side.

Bob, I need some help with the felt installation. I'm thinking the felt that rubs on the spindle starts in the threaded hole (with brass plug) at each end of the casting, passes through the where the two ends of the felt tube join and the curl around to make contact with the spindle. There is also some string attached to the felt wick, does this tuck under the felt tube (top of the casting) and act as the wicking for the lubricant from the felt tube to the spindle?

Simon