Is knurling hard on bearings?

[HMF]

Is knurling with the old style "side-load" knurling tool REALLY as hard on bearings as people make it out to be?
Has there ever been an actual instance where bearings have failed or gone bad due to side-load knurling?

Thanks,

Nelson

 

[jgedde]

It depends on the bearing type/size in your headstock - some bearing types don't like side loading. Old style babbitt bearings, especially ones with a thrust surface, certainly don't like it. Tapered roller bearings can take it.

IMHO, bump knurling is hardest on the compound and cross slide gibs/ways. On my old Atlas, bump knurling would almost universally require me to do a gib adjustment afterwards. I had best luck knurling by setting the compound angle perpendicular to the workpiece (so it feeds like the cross-slide).

I haven't tried knurling with my Grizzly lathe. But, it's vastly more rigid than the Atlas.

John

 

[jgedde]

I don't mean the acme screw and nut, as they should be immune from any ill effects. My Atlas has small gibs, and the knurling force tends to try and rock the compound on its dovetail and the gibs and gib screws take all the force. This universally leaves them loose afterwards - at least it does for me. Same thing happens when I part off. Turning the compound perpendicular to the workpiece makes a big difference.

I suspect this may be a problem on most small lathes (Sherline, Sieg, etc) and larger poor rigidity lathes like my Atlas.

All in all, as a generality, I'd say that bump knurling should be reserved for larger machines, but if it works for you then by all means it doesn't justify the expense of a straddle knurling tool. I use a bump knurler myself but also know that the Atlas doesn't like it much - you can actually see the cross slide moving in its dovetail. Tightening the gib to eliminate this works, but makes the cross slide virtually immovable afterwards.

Then again, I'm passing judgement based on an Atlas which is a known flexible flyer. Our Monarchs here at work bump knurl with no issues at all. Tonight I'll knurl something up on my Grizzly - I suspect it will be problem free.

By the way, I've started using convex, diametral pitch knurls (as opposed to circular pitch). These things are a dream! The convex knurl is terrific and the Atlas doesn't "complain" nearly as much as they require less force and are designed to be axially fed. They're expensive, but you'll have a set for a lifetime in an HSM environment. I bought the 64 DP set - the ANSI "recommended" 96 DP knurls are too fine for my tastes.

The convex 64 DP knurls also track without "mashing" on diameters in 1/64" increments. Here's what I use: Accu-Trak Convex knurls 3/4x3/8x1/4

John

 

[Zigeuner]

I will occasionally knurl some aluminum with my side knurler. My lathe is a 13 X 40 with -200 BXA QC Holders. It does a nice job without much trouble.

The spindle bearings on the Enco are approximatey 4" in diameter (100mm) with a central bore of 1-1/2" (38mm). I doubt that side knurling would put any more side force on the spindle and its bearings than the weight of the spindle itself while making a deep cut.

If I did nothing but knurling, I'd probably get the scissors type of knurler anyway. They are rather expensive and for occasional use, I really don't need one.

 

[November X-ray]

If you have a side type knurl it is easy to make some extensions and convert it to a squeeze type. Using some 3/4" key stock I made a couple of arms to extend the one that came with my QCTP and I use a simple hand squeeze bar clamp to put the pressure on it. works good so far on aluminum, brass and steel although I only knurl occasionally.

 

[Zigeuner]

I do a fair amount of knurling. Many of the parts I make are knobs and tools and whatnots that are to be manipulated using hands and fingers. Knurling the surface is good for that. I have three types of knurlers: bump (from one side), scissors (squeeze type), and a cut type knurler. Quickest and easiest to set up is the cut style which is why I prefer to use it. Scissors is next in order of preference. Bump is the lowest.

Bump style knurlers use very high side loads. MUCH higher than regular turning. Not only is it hard on bearings but it is also hard on the work and the chuck. Especially a 3-jaw. It can also be hard on centers (live or dead) if one has to knurl far from the chuck. Already mentioned was loads on carriage bearing surfaces and cross feed screws. I don't know about plain bearings but any tapered or ball bearing should be able to handle the loads easily.

Cut style knurlers are really very neat. When set up properly the side loads are similar to regular turning. The down side is the knurls are expensive have to be sharp and the knurling tools are very expensive. There was a couple of articles about a year ago in one of the hobby machinist magazines on how to make ones own cut style knurling tool. Very good article and a very nice tool. Worth making for even the most casual of hobbyists IMO.

Scissors type knurlers, when st up properly have practically zero side loads on the spindle bearings. The thrust loads on the spindle bearings are pretty high but nothing the bearings shouldn't be able to handle. The domestic knurling tools can be expensive but there are plenty of reasonably priced imports available that seem to work well.

A lot depends on the quality of the knurls themselves. More quality costs more dollars.

On any type of knurler on any type of material always keep the knurls dripping wet with cutting fluid. Either by a pump system or with a can in one hand. It keeps the knurl bearings lubricated, flushes the mashed up chips away, and makes for a much better finish.

Nothing like a nice crisp knurl on a part to make it look good.

-DU-

Sure, cut knurlers are great. They are also rather expensive. For occasional use, there's no point to it, expecially for a hobbiest. .

I would happily accept your opinion that side knurlers are hard on bearings if there where some scientific proof or even some empirical data. Unfortunately, there is none. It's one facet of the old philosophical problem of cause and effect. "Gosh, the lathe spindle bearings on my WWII Pratt & Whitney 20 X 72 wore out. It couldn't have been the 800,000 Grumman Hellcat aileron bushings that were made on it between December, 1941 and June 1945 or the fact that it sat outside in a government corporation yard for 18 years before I got it in that auction. There was some rust on it from the flood in Peconic Long Island that year, but I'm sure it was that side knurling that I did a couple of times with my ENCO side knurler. That's got to be it and I thought it would last forever.".

 

[4GSR]

"if there where some scientific proof or even some empirical data."

From an engineering stand point, it is by calculations, which would take me years to do, that plain bearings can handle higher loading than any antifriction bearing can handle. ++++++

I personnaly do not like crush knurling on any of my lathes. I've always used a old medium diamond knurl cut knurling tool Dad "borrowed" many years ago from work to knurl with. I can't even find knurls that will fit it today, some Swedish made knurling tool. I have one of those Aloris ones that has never worked for me! Just bought one of those "sissor" style ones, haven't used it yet.

Ken

 

[ScrapMetal]

Okay guys, I give. The few "cut knurling" setups I've seen still look pretty much like the bump knurlers. Why is the side force on the bearings so much less?

Thanks,

-Ron

 

[Zigeuner]

Okay guys, I give. The few "cut knurling" setups I've seen still look pretty much like the bump knurlers. Why is the side force on the bearings so much less?

Thanks,

-Ron

I'm only guessing here. If there is less pressure with cut knurling, and I have no data, it mght be that the teeth are sharper and cut more smoothly into the metal, thus requiring less pressure.

In any case, this entire issue is a tempest in a teapot as far as I can see. The machines that we have are made to be used. That means that they will inevitably wear and perhaps, someday, wear out.

If you want to see some side pressure, watch a 20" lathe take a half inch cut off of a steel roller with a large carbide tool. Now that's side pressure!

 

[ScrapMetal]

It's making sense now. Drats! Now I have another "tool desire", a cut knurler. Time to start scanning the funny papers.

Thanks guys,

-Ron