Help for a woodworker

Anyone who has a reasonably sized metal lathe should be able to chuck it up and polish off the excess in a 1/2 or so worth of time.

But most folks are going to want you to remove the sanding drums.

And I think that's 1/2 hour?

What makes you think that ?

If you can't find a machinist that isn't an unreasonable amount of metal to remove with a coarse file and sandpaper. First drawfile lengthwise flats, using their width to gauge progress and keep the cut depth constant, then sand down the ridges between the flats with a long narrow strip of sandpaper. If you darken the metal with laundry marker or candle flame soot it's easy to see where the file is cutting.

You could do only the very end until the bearing starts on, then work down the shaft. Darken the shaft, jam the bearing on and remove it, file off the contact marks. This is fairly quick if you are within a thousandth.

It's like the final stages of rounding a sailboat mast:

Here is a hand-held tool that finishes shafts to very precise diameter: could make a wooden one by boring a 1" hole on the joint between two strips of wood and lining it with sandpaper, or just clamping one end of the sandpaper betwen the wood strips, leaving the other end free in the hole. Spin the shaft and slide the tool back and forth. They cut very round but not necessarily perfectly straight, and they tend to cut deeper on the ends where you reverse direction.

jsw

First start with where are you? Someone that frequents RCM might be willin= g to help.

Second I agree with Jim Wilkins you can do it your self. Since you are a w= ood worker, do you have a wood lathe it would fit in? If so put it in the = lothe and use sandpaper on the tailstock end to get it the right side. I s= ay do the tailstock end as the headstock end might be held with a 4 jaw chu= ck and may not be centered perfectly. After you get one end done, switch t= he work so the other end is at the tailstock.

No wood lathe, then make a couple of vee blocks out of some wood and figure= out a way to drive the shaft. A vee belt will work even though not in a g= roove like a pulley. You are going to polish it with sandpaper, not cut it= with a tool bit. Set the vee blocks inboard of the areas you need to poli= sh down.

Last week I help take the rust off a shaft so the bearings would fit. For = that the thing that worked best was just sandpaper. The shaft was about ei= ght feet long and an inch and a half in diameter and had a four foot diame= ter pulley on one end. So popping it a lathe was not something easy to do.= We just removed the rust while the shaft was sitting on saw hourses. It = did not take long after getting the sandpaper. I would guess you could do = what you need to do in a hour or so. But I always think things will go fas= ter than they do.

Dan

If the inner race of the pillow block freely spins, light or moderate pressure with a small die grinder on the ID might get you there more quickly. More easy to modify the pillow block.

I don't know about the other guys, but if I were you, I'd spring a few extra bucks for a piece of precision-ground shafting. It's not all that expensive, and it will be accurate in diameter and _straight_. The cold- rolled stock will not be straight no matter what you do to the ends, unless you turn the entire length with a proper metal lathe with follower rest.

McMaster-Carr, MSC, SpeedyMetals, and a number of other places carry the stuff.

LLoyd

...

I agree. You do NOT want your roller to have any eccentricity or bowing. OK, you're always going to have some, but you want to minimize it as much as you can.

McMaster-Carr has a 1" x 42" for $52:

might seem like a lot (especially if your costs have been more that expected), but it will be well worth the avoidance of a bump-bump-bump sander.

I would have walked into the local bearing supply store and tried their shafting in their pillow blocks.

few weeks ago they sold me 1" x 36" CRS shafting for $18, and pillow blocks were ~$12 at a second nearby supplier (of 3) a few years ago when I built the sawmill. They sell shaft with full-length keyways so you can slide on a drive pulley or Lovejoy coupler without machine work.

While I was buying the pillow blocks an alternate-energy inventor came in to pick up the 2" bearings he had ordered to go on 2" water pipe. You think you have a mismatch??

jsw

I don't know why he working with a hollow shaft, how the disks are attached and what RPM will be. Maybe he's working with a small budget and just trying to use materials or parts that he has on hand. It seems that for putting disks on a hollow shaft, they might have to be welded on to prevent them from spinning on the shaft. I'd also worry about the torque on the shaft and flexing under load.

If I was building from scratch, I'd do what you said and maybe get a shaft with a keyway like this:

I was expecting to get flamed for my suggestion because I know the danger of throwing the bearing off-center. I've worked with limited options in the past and sometimes do what I can to get by.

-If the inner race of the pillow block freely spins, light or moderate

-pressure with a small die grinder on the ID might get you there more

-quickly. More easy to modify the pillow block.

More quickly perhaps, but you have little control over the diameter, straightness or concentricity. Grinding the shaft by hand has the same difficulty.

With filing you can remove half the excess diameter, measure the width of the resulting flat, and copy it all around. Then file down the ridges between, to an equal width of all the flats. Taper in diameter shows up as taper in the width.

See why we buy home shop metal lathes after trying to work metal without them?

jsw

I disagree. Yes the precision ground shaft would be better, but not by ver= y much. As long as the shaft is stiff enough, it matters little how straig= ht it is. Once he has the shaft mounted in the bearings , he can true up t= he disks so they run perfectly true. At least he ought to proceed with wha= t he has. If he finds there is a problem with balance or vibration, he can= always go to precession shafting.

Dan

I know what you mean about metalworking tools and I think that you appreciate what it means not to have them as I do.

After I posted, I thought more about opening the ID of the pillow block.

I think that if you mounted it to a board and then attached some light gauge angle iron to the board you could use it as a guide for a small grinder and maybe improve over doing it free-hand. Food for thought anyways.

-I think that if you mounted it to a board and then attached some light

-gauge angle iron to the board you could use it as a guide for a small

-grinder and maybe improve over doing it free-hand. Food for thought

-anyways.

Even then variations in bearing friction or seal drag will cause speed and thus depth of cut variations.

The early machine tool builders tried all sorts of trick like that to avoid the expense and difficulty of making and machining heavy iron frames. There is an 1830ish lathe in the American Precision Museum with a granite bed, with thin steel(?) strips grouted into grooves in the top to guide the carriage.

Eventually they gave up on self-guided cutters in favor of very rigid machine ways.

jsw

On 6/29/2012 1:22 PM, snipped-for-privacy@krl.org wrote: ...

I'd worry more about the hollow shaft and stiffness, indeed. Not sure why one would make that choice...

--

Maybe you're right. I was thinking more along the lines of centerless grinding.

Depends on the shop, of course. Some won't touch it with a 10 foot pole, others will charge an inflated price in the hopes you'll go elsewhere, the one you want to find will do it for $20-50 or a case of beer. Try calling some local shops, and if they don't want the work, see if they can tell you who might - some retired guy with a lathe in the garage is probably the guy you want, not a place with $100,000 "machining centers." An auto or tractor mechanic might know who you need to find.

On the crude end, if you have a wood lathe that the thing fits in you could mount it up and file or sand it. Not spiffy, not correct, might get it done well enough. Cover the bed and clean up the wood shavings first, so you don't start a fire in the wood shavings or end up with metal and grit in the bed.

You probably don't even want a "perfect" fit - a slight interference (light press) fit is likely better, but I think that's more like 0.0005" on an inch rather than 0.005" (been a while since I have used that knowledge, and I find it's faded a bit = perhaps someone else can fill in.)

" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:

Dan, even if the end-disks run true, if the shaft is not straight, it will vibrate like a bitch at sanding speeds.

LLoyd

[ ... ]

And even if by some miracle it *is* straight when you start, it is not likely to be so when you finish. Cold rolled steel has stresses from the rolling process, and when you machine away the surface, it usually distorts from no longer having to fight those stresses.

Enjoy, DoN.