Spindle Runout

[Mermaid]

Hi all. This is my first post so please bear with me. I own a six year old 2227L Craftex lathe and have noticed that my surface finishes aren't as good as they used to be. I have also noticed that the machine sometimes cuts a very slight (0.0003" over 2.0") taper on cylindrical work. My tools are sharp and centered. The cross slide, top slide gib adjustment as well as tool post tightness have been checked. The last straw was in cutting a 40 T.P.I. thread in W1(carbide treading tool) . The thread flanks were quite ragged. The part is usable but not pretty so I'm not a happy camper . The lathe has been only lightly used and well cared for. I'm using SAE 20 non-detergent motor oil in the head stock. Just this morning I set up my DTI and found APR 0.0003" lateral slack in the spindle bearings They are # 32009 (chuck end) and # 320 taper roller bearings.

Since these are rolling element bearings I would expect that they would have some working clearance but I'm not sure how much is allowable. The bearings are adjustable but I don't have the required spanner wrenches so I'm going to have to make a pair if I have to make the adjustments. Are bearing adjustments required or could there be another cause for for these problems?

[J Tiers]

Clearance is generally BAD. Leads to chatter and bad finish (there are also many other reasons for a ragged finish, however).

Your bad finish may not be due to clearance, but I would generally expect there not to be any clearance, totally independent of any other issues.

Most any spindle bearing is expected and intended to have "negative clearance", or "preload", to actually have an axial load on the bearings adjusted-in by the nut at the end of the spindle (or, in other cases, by having different length spacers on the spindle and in the recess the bearings go in). For lathes, the adjusting nut is the most usual.

There may be an adjustment procedure in the manual.

[BCRider]

Another vote that it sounds like you need to make a pair of those wrenches and eliminate the slack that is producing the play.

Another possible issue MIGHT be that the bearings themselves have become very slightly loose in the head stock housing. If so tweaking the bearing preload may not eliminate the play you found.

But for now I'd look at making up a pair of C wrenches and check the axial preload. If it still has some play then you might need to look further into how well the bearings are seated in the headstock casting.

[macona]

What kind of carbide threading tool. If it is just one of those brazed tools on a shank, well, those are crap as stock and must be sharpened before use. And tool steel does not machine that well.

[dian]

0.0003" "lateral slack"? how did you come up with that number? every time i breathe on my mitutoyo 0.001 mm indicator, it will show a deviation of similar magnitude.

[darryl]

Three tenths over 2 inches is not bad, but it might have been better from the start. It could be that some play has developed in the spindle bearings, or perhaps the headstock has shifted very slightly on the bed. I don't know how yours is held in place, but without making any adjustment to it, perhaps you might tighten the holding bolts. You'll find while doing this whether there was some looseness there. If there was, then you could legitimately think that this could have been part of the problem.

A usual test is to indicate from a bar held in the chuck, then apply hand pressure to the chuck. Up, down, front to back- you'll see some movement and it should all be flex, nothing where there's more than one rest position as shown by the indicator. I've never heard or read of doing this test by applying hand pressure against the head stock, but why not try that too. Try to twist it without pushing it backward or forward- see if there's any movement and if it comes back to 'zero' each time.

Re the bearing races moving in the bores- if there is some play, perhaps some oil wicked into these areas would provide some damping of vibrations. That won't correct a deviation, but it would help to provide dynamic stiffness. I don't know how much you can actually get at without disassembly, so this is just a suggestion. As far as adjusting preload, you'd want to be pretty careful to not create the situation where the bearings get too warm after running for a time.

[macona]

Get some 1144 or 12L14 and see how that turns. Tool steel threads like crap. Dont use the stuff unless you actually need to make hardened tools. If you just need precision stock to build off of you can order TGP (turned, ground, polished) stock in a lot of different alloys, I picked up a chunk of 1-1/2" 1144 TGP for a press ram at work and the stuff machines beautifully.

I think you are expecting too much out of a little lathe like that.

[J Tiers]

Get some 1144 or 12L14 and see how that turns. Tool steel threads like crap. Dont use the stuff unless you actually need to make hardened tools. If you just need precision stock to build off of you can order TGP (turned, ground, polished) stock in a lot of different alloys, I picked up a chunk of 1-1/2" 1144 TGP for a press ram at work and the stuff machines beautifully.

I think you are expecting too much out of a little lathe like that.

1) The machine is a 10" swing by 18" C-C. Not a "little lathe". More of a "mid-size", that should be expected to do decently.

2) Size has not one thing to do with quality of machining possible, all it really affects is usable size of workpiece

3) While SOME tool steel does not machine well, I have found that quite a lot of it actually is quite nice to work with. I'd rather work with it than the softer gummy aluminum alloys, or 1018.

[garyhlucas]

If it has tapered rollers I'd put a dial indicator on the bed and against the face of the chuck. Then I'd use the carriage handwheel to push against the chuck firmly, like you were taking a cut. I would expect to see no or hardly noticeable movement on the indicator. If it moved a measurable distance then I'd adjust the preload. I'd probably take out the motion indicated, plus another 0.0005". I'd check the pitch of the adjusting nut to figure out how much of a turn to make.

[enginuity]

I have the exact same lathe.

There should be no lateral play. This indicates the bearings have lost their preload. The spindle should have some friction when you turn it in neutral.

Adjusting preload on small import machines is often needed to be done. Brian Rupnow has a post awhile back where he was dealing with vibrations on a Busy Bee lathe that was solved with adjusting the preload.

They tend to leave it loose from the factory to prevent overheating of the bearings. Over time it tends to relax. Incorrect preload will lead to very poor surface finishes.

Tighten up the preload and monitor the temperature of the bearings.

The lathes aren't super small lathes and are a copy of the Emco 10. I would prefer an Emco, or a Hardinge HLV, but for what they are they do well. The tapered roller bearing headstock is a good design and is very rigid. The carriage is very rigid for the size of lathe.

The biggest down fall of the machine is the lack of power crossfeed and the lack of a slotted leadscrew putting strain on the half nut. Busy Bee has really jacked up the price on these machines over the years and generally you can sell them for what you paid for them if you take care of it.

[old mart]

As said before, a small amount of preload is normal for taper rollers. The usual empirical test is to run the lathe at max speed and feel the temperature rise in the area of the bearings. If after 20 minutes, the rise in temperature is more than luke warm, say 20F higher, then you may be too tight. Check every 5 minutes just to be safe.