I am finding it very difficult and frustrating to get bowl blanks (trimmed from half-logs) balanced so that they don't shake the lathe when first mounted. I am limited in how much excess I can trim off before attaching the face plate so I have to mount, see if the blank is out of balance, remove and move the face plate in some direction, remount and see if it still wobbles and shakes the lathe. Since the blanks are anything but symetrical, finding the "center" for the face plate takes a lot of time. I have tried balancing the blank on a point to see which way the weight tips it but even this doesn't seem to help much - it's pretty much trial and error until I get it close enough so that it is safe to turn. I use the tail stock to help stabalize the spin but I am losing a lot of time trying to find the sweet spot. Thanks for any suggestions.
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Difficulty balancing bowl blanks
- Thread starter Keith
- Start date
Start between centers
Hi Keith,
I usually start with the bowl blank between centers. This allows me to shift either or both centers slightly until the best balance point (or desired blank orientation) is found. I first turn the lathe slowly by hand to see if I'm close, and then turn it on at the slowest speed before ramping up to the start of vibration and then backing off slightly. I then turn a tenon for a chuck, or you could turn a flat spot for a faceplate.
Hi Keith,
I usually start with the bowl blank between centers. This allows me to shift either or both centers slightly until the best balance point (or desired blank orientation) is found. I first turn the lathe slowly by hand to see if I'm close, and then turn it on at the slowest speed before ramping up to the start of vibration and then backing off slightly. I then turn a tenon for a chuck, or you could turn a flat spot for a faceplate.
john lucas
AAW Forum Expert
Keith I start all bowls between centers so I can shift it easily to help stabilize it. I also purchased a cheap electric chainsaw to cut off really offcenter protrusions.
Take your best guess at the orientation you want. Rotate it by hand and change either the drive center or tailstock until you get it just the way you want it. Then I crank the tailstock in and with the headstock locked I rock the wood back and forth while cranking the tailstock to seat the drive center better. Then I rough out the outside and turn a tenon for my chuck. If you are using a faceplate turn the tenon to the same size as the faceplate. This makes it easier to align the faceplate properly.
Since I'm using a chuck I usually completely turn the outside of the bowl except for the bottom where the chuck goes. Then mount it in the chuck and turn the inside.
Then I put a rubber sink stopper over the chuck and put the open end of the bowl over this. Bring the tailstock up (you still have the marks from the tailstock when you first mounted it) to hold it in place and turn the bottom to shape all except a little stub for the tailstock. This you carve off.
It sounds like your lathe won't go to slow enough speeds. My first full size lathe was a Delta 46-700. Slow speed was 500 rpm and it would walk all over the shop with even small blanks. I didn't know you could start a bowl between centers and usually mounting the faceplate was guess work as you've found out.
Take your best guess at the orientation you want. Rotate it by hand and change either the drive center or tailstock until you get it just the way you want it. Then I crank the tailstock in and with the headstock locked I rock the wood back and forth while cranking the tailstock to seat the drive center better. Then I rough out the outside and turn a tenon for my chuck. If you are using a faceplate turn the tenon to the same size as the faceplate. This makes it easier to align the faceplate properly.
Since I'm using a chuck I usually completely turn the outside of the bowl except for the bottom where the chuck goes. Then mount it in the chuck and turn the inside.
Then I put a rubber sink stopper over the chuck and put the open end of the bowl over this. Bring the tailstock up (you still have the marks from the tailstock when you first mounted it) to hold it in place and turn the bottom to shape all except a little stub for the tailstock. This you carve off.
It sounds like your lathe won't go to slow enough speeds. My first full size lathe was a Delta 46-700. Slow speed was 500 rpm and it would walk all over the shop with even small blanks. I didn't know you could start a bowl between centers and usually mounting the faceplate was guess work as you've found out.
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Have chainsaw but no bandsaw? I see a lot of people who won't trim off the waste at the ends of the log, something I even do it on the bandsaw. http://i35.photobucket.com/albums/d160/GoodOnesGone/Trim-for-Balance-2.jpg http://i35.photobucket.com/albums/d160/GoodOnesGone/Trim-for-balance-1.jpg No sense beating up the lathe and potentially myself if I "start between centers" and dismount the blank because I hooked the heavy end. Since the heaviest part of an untrimmed blank is the farthest out, and it unbalances by the SQUARE of the distance, even a bit of trimming can mean a lot for balance. Undercut it with the chainsaw. Takes no great precision. When you get your bandsaw, the habit of undercutting will add a couple inches to the height of cut available, too.
If you decide to use your spur center, do yourself a favor and counterbore about a quarter inch so you won't dismount the blank by chewing it or hooking it with the tool. Every time you tilt to regain balance at the tapered end you unbalance the large end, of course, so keep a scrub plane, drawknife or spokeshave handy for reducing protrusions that hit the bed or unbalance the piece.
If you get one of those cuts through a log at right angles to the way it was on the ground, you may have one soaked side and one dryer side. No hope there except to hang some perforated sinker lead into what will become the open area on the other side. Lag bolts my preferred method of attachment.
If you decide to use your spur center, do yourself a favor and counterbore about a quarter inch so you won't dismount the blank by chewing it or hooking it with the tool. Every time you tilt to regain balance at the tapered end you unbalance the large end, of course, so keep a scrub plane, drawknife or spokeshave handy for reducing protrusions that hit the bed or unbalance the piece.
If you get one of those cuts through a log at right angles to the way it was on the ground, you may have one soaked side and one dryer side. No hope there except to hang some perforated sinker lead into what will become the open area on the other side. Lag bolts my preferred method of attachment.
Balancing Bowl Blanks
My thanks to those who replied. Even though I knew the blank was secured between the centers, all that spinning wood is a little more scary without a face plate and screws to hold it. However, I followed your suggestions, including counterboring for the spur center, and everything worked out fine. Certainly, it took a lot less time to get going, which was great. Thanks for your help.
My thanks to those who replied. Even though I knew the blank was secured between the centers, all that spinning wood is a little more scary without a face plate and screws to hold it. However, I followed your suggestions, including counterboring for the spur center, and everything worked out fine. Certainly, it took a lot less time to get going, which was great. Thanks for your help.
It is common, at least for me to have blanks that are perfectly centered, but not balanced. That is just the way wood is. That is one of the benefits of true variable speed. If you have a belt drive, and disengage the belt, the heavy end will go down, but no matter how you do it, you will have to fiddle around to get it close.
robo hippy
robo hippy
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I do a lot of natural edge hollow forms and choose unbalanced blanks to get nice contours for the opening lip.
I cut the blank round on a bandsaw or hexoganal with a chain saw.
for the chain saw "round" I draw two circles. the desired blank diameter and on 2" larger. I then make chainsaw cut that cut away all the big circle and leave all the small circle. Usually a hexagon does that if not I cut a "sixteenagon"
I mount this blank between centers. I balance it for weight first.
One side will drop to the down side. I move the heavy side to the top, loosen the tail stock, and let the blank rotate downward moving the heavy side closer to the center of rotation.
doing this 2-5 times balances the blank so that one side is not much heavier than any other and the piece can be spun slowly all the way around without favoring a heavy side.
after a quick roughing round, I adjust the blank for grain alignment or to adjust a rim feature. I do this by loosening the tail stock and letting the piece drop down a bit. then slow the lathe down and rough it round again as it will have been made out of balance again.
happy turning,
Al
I cut the blank round on a bandsaw or hexoganal with a chain saw.
for the chain saw "round" I draw two circles. the desired blank diameter and on 2" larger. I then make chainsaw cut that cut away all the big circle and leave all the small circle. Usually a hexagon does that if not I cut a "sixteenagon"
I mount this blank between centers. I balance it for weight first.
One side will drop to the down side. I move the heavy side to the top, loosen the tail stock, and let the blank rotate downward moving the heavy side closer to the center of rotation.
doing this 2-5 times balances the blank so that one side is not much heavier than any other and the piece can be spun slowly all the way around without favoring a heavy side.
after a quick roughing round, I adjust the blank for grain alignment or to adjust a rim feature. I do this by loosening the tail stock and letting the piece drop down a bit. then slow the lathe down and rough it round again as it will have been made out of balance again.
happy turning,
Al
Similar to these, but I use a Lancelot (small chain saw) in a right-angle grinder. Identify the heavy parts by drift test. I place two opposing wedges (cut from 4x4 timber) between the workpiece and the bed to hold position while trimming - less load on a spindle lock, if I had one.
Maybe also consider weighing down the lathe stand to reduce the rock and roll.
odie
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Good point, rsser......
Sometimes, the obvious isn't always recognized.......because all those dag-blasted trees get in the way of seeing it! Heh,heh,heh!
Adding weight is a common way of tackling the "rock and roll". For my own needs, I've simply chosen a very sturdy and heavy lathe that is securely bolted to the concrete slab floor.......works for me!
I think some turners might be overly concerned about wear and tear on their spindle bearings, but they fail to see this is only a momentary consideration.......the out of balance condition immediately improves, once you begin removing wood in the right places!
ooc
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Good point, rsser......
Sometimes, the obvious isn't always recognized.......because all those dag-blasted trees get in the way of seeing it! Heh,heh,heh!
Adding weight is a common way of tackling the "rock and roll". For my own needs, I've simply chosen a very sturdy and heavy lathe that is securely bolted to the concrete slab floor.......works for me!
I think some turners might be overly concerned about wear and tear on their spindle bearings, but they fail to see this is only a momentary consideration.......the out of balance condition immediately improves, once you begin removing wood in the right places!
Weighting is the third best thing as I see it. Best is to cut at minimum rpm. Those of us with belts to dink with can even take a little tension off of them so that we spin a bit slower under load. I like broad shavings as a way to get down to round, but I won't change cutting angle, just pressure to slip the belt.
Second best is to broaden the footprint of the lathe, forcing it to try to compress the incompressible. Had one lathe at school that wasn't tied down that benefited from laying the hip into the stand just beneath the ways in front. Sort of the "steady rest" principle, I guess.
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There is another step that must be done before securing the wood between centers and that is statically balancing the piece. Once it has been statically balanced, there will be very little vibration when it is secured and turned between centers.
In order to statically balance the wood, only the center point at each end touches the wood -- do not let the drive spurs touch the wood. If out of balance, the wood will always rotate so that the heavy side is down. When balanced, the wood will stay wherever it is rotated.