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View Full Version : runout ? having a 6 foot shaft turned



partcat
02-09-2005, 08:24 PM
Hello and thanks for any replies.I am having my sawmill arbor turned down and when I dropped it off to the machine shop the machinist said that the chuck had 12000ths runout.could someone tell me if this is alot and will my bearings fit properly.thanks james

Dave Opincarne
02-09-2005, 08:53 PM
Twelve thousandths as in 12/1000" or .012" That's a lot IMO. It doesn't mean the part will be that sloppy, but that the new diamater will thereticly be off center by that amount.

Dave

partcat
02-09-2005, 09:03 PM
thanks Dave he said 12000ths of an inch.I think that is .012. thay haven't started machining it yet.Would you recommend finding another machine shop.I am paying 200 to have an 1/8 inch taken off the diameter.thanks James

jburstein
02-09-2005, 09:10 PM
what you are referring to as "12000ths of an inch" is commonly notated as "twelve thousandths of an inch" as in 12 * .001" = .012"

-Justin

egpace
02-09-2005, 09:36 PM
Acceptable runout depends on the application. The higher the speed the less runout you should have.
Ask the shop if they have a 4 jaw independent chuck. (Not much of a shop if they don’t). With a 4 jaw independent chuck they can just about eliminate any runout.

Ed

partcat
02-09-2005, 09:54 PM
thanks Ed , they don't have a different chuck.He said they needed a new one . I think I will go back and get it and take it elsewhere.thanks , James

G.A. Ewen
02-09-2005, 10:01 PM
Why are you paying to have it turned down instead of buying a shaft of the correct size?

partcat
02-09-2005, 10:16 PM
I am having the shaft turned down becuase it is an arbor that has a collar milled on it at one end with threads.Its for a sawmill.It had babbit bearings and is 2 7/8 .I found that this isn't a standard size shaft that they make pillow block bearings for. I purchased 2 3/4 inch bearings and thought this was the best route. thanks james

Mike Burdick
02-09-2005, 10:31 PM
James,

I don't know why the chuck runout would be of any concern since a 6-foot shaft would most likely be turned between centers.

Anyway, all you are really concerned about is the short distance where the shaft holds the bearing - that needs to be machined very accurately for what I would assume is a press fit.

I think I would check with the machine shop again so you can be sure what they are doing. I think there is some miscommunication here.

snowman
02-09-2005, 10:33 PM
Ask them to make you a bushing of ID 2 7/8 with OD of 3, or even 3 1/4. You might even be able to buy a bronze bushing and have it brazed on.

Then use pillowblocks of 3 or 3 1/4...unless you've already bought 2 3/4 pillowblocks and can't return them http://bbs.homeshopmachinist.net//smile.gif

Seems lots easier!

Is this a bandsaw or circular type saw?

-Jacob

partcat
02-09-2005, 10:48 PM
Jacob already purchased the bearings and the shaft was worn do to the babbit bearing being contaminated over time. this is a circular mill. I am doing this on a shoestring budget and the bearings i purchased i found on ebay for 50 bucks they r new sealmaster type E pillow blocks which r a heavy bearing,they cost 400 each retail.thanks James

partcat
02-09-2005, 10:55 PM
Mike yes it is being turned between centers.The machinist said to me that one end would be a slip fit and the other tight for the bearings. Thats really my question does this runout matter.This arbor will turn 700 rpms.Would this effect the collar on the arbors sguareness to the shaft at all.It will have a 56 inch blade .thanks james

Mike Burdick
02-09-2005, 11:08 PM
James,

Runout only produces a taper - the shaft will still be balanced! (Since he's turning it between centers the chuck, if used at all, will only be used to hold the dog.) However, if there is any runout in the lathe's bearings, the taper will be a problem only for the bearing seats. Just talk to the machinist again before you have them do it. If what he says doesn't make sense - then take it to someone else.

Replacing the shaft and babbit bearings with ball bearings is sure going to be nice. I did that same thing to a "buzz" saw (6-foot blade) that I use for cutting firewood. Runs real quiet now and doesn't get oil all over me. http://bbs.homeshopmachinist.net//wink.gif

___________________



[This message has been edited by Mike Burdick (edited 02-09-2005).]

Kansas_Farmer
02-09-2005, 11:12 PM
I think at 700 RPM you won't have a problem with runout. With that size of blade I'd be more worried about the shaft flexing between the bearings when you load it up. How many bearings on this 6'er? 2 or 3? To me, I'd like to have a center carrier bearing in there to keep the shaft straight.

I built up a sawmill for a guy where his arbor was only about 40" long with 2 bearings. The powerplant was a QXD3 Herc I6 60hp engine. The Blade was 32" and turned at 1000 rpm. With a load on it, the arbor would bend in the middle or setup an ossilation. The end result was typically a pitched belt. Anyway, this is why I'd like to see 3 bearings in it.

FWIW

partcat
02-09-2005, 11:21 PM
kansas farmer I am looking for a 3rd bearing.I agree, it is in my plan although I haven't located one yet.I am also not against using a smaller blade in the future if i find one . thanks james

wierdscience
02-09-2005, 11:29 PM
From having turned more than one saw mandrel my advice would be to mark the locations of the pillowblocks and the pulley on the shaft.He can hold the areas where they will land to a +.0000/-.001 size.The rest of the length can be .005-.008" undersize,since it has nothing to do with the bearings.

After the mandrel is mounted in it's bearings in the mill,power the mandrel and face the saw flange true with a grinder mounted in a slide vice to achieve perfect runout.The flange rounout is critical as even a small amount there will translate into a lot on the rim of the blade.

On the type E pillow blocks be sure and use the factory recomended lube,wheel bearing or bucket and pin grease will kill them in short order.

partcat
02-09-2005, 11:39 PM
Mike thanks and I will do that.yes ball bearing were a much easier solution than having to worry about bearing wear.This is an old knight mill that was all babbit.I have replaced everything i could with ball bearing.I am running the head blocks with a gear box that has a straight thru whole that allows me to run the 1 15/16 shaft that works the racks.I can turn the input shaft by hand and move the blocks. I am hooking up a gear reduction motor to that and using a forward reverse switch.thanks mike james

partcat
02-09-2005, 11:47 PM
wierdscience thanks . yes I understand that the collar runout is critical.I hope I don't have to grind on it.I will look into the bearing lubricant.Thanks, James

madman
02-10-2005, 02:14 AM
Should be a max tir of .002 If thats not possible take it to a real machine shop with a real machinist working in it. Get an old bastard they know everything.