Having returned to turning for the first time since school, (many years ago) and have managed to full our house with many small bowls, hollow forms, couple of lamps, pens, and some thin platters etc. using up all my hoarded timber. Four months into this renaissance, I have recently started to spot my work pieces "wobbling" whilst spinning, made very apparent when attempting to cut a 4 x 1mm groove and inset a contrasting band near the rim of a part-turned (outside only) 8" sycamore bowl blank (faceplate mounted), and was even more apparent when reversed and "chucked" The lathe, tools and my current experience are all four months old, and the "wobble" seems progressive. The lathe bearings, and the chuck have just been checked by the supplier (Axminster) and found to be well within tolerance. Thus they have decided, the problem is me! Any help, what am I doing wrong?
You say the blanks are faceplate-mounted, and that the wobble is progressive. it sounds as though the mounting is getting looser as you turn the blank. If the blank is screwed to the faceplate, double check the screws. If you are using a sacrificial blank between the faceplate and the turning blank, see if it is getting loose. Good luck, Dave in Fairfax
Thankyou gentlemen, Have checked headstock to lathe, I'm 14stone odd and can't move it when tightened, and have tried two different faceplates with long and short #8's in an attempt to isolate the problem The lathe (M900) has a home made shelf under with 50k of cement in bags (a hint from this newsgroup) and is rawbolted to a concrete (bloody cold) slab floor. Even turning small items I can see the eccentricity.
Given that you have checked all this, I would recommend you change the bearings.
I once heard of an car or airplane component sourced from two different countries. The one lasted several times as long as the other. Both were within tolerances. The longer-lasting one, however, seemed to have all parts machined with no detectable variability with the accuracy of gauges, while the other varied, but all within specs. Maybe the bearings are wearing and while "within specs" they are causing vibration.
Also, when remounting in the chuck, have you tried rotating the piece in the chuck a quarter turn at a time, tightening and spinning under power until you get the lowest deflection/vibration mounting?
Phil; Is there a possibility that the headstock lathe spindle is bent? A bowed shaft would give those symptoms. It is possible to bow a lathe spindle by over tightening a pulley set screw - if the pulley hole is irregular. I had a lathe once with this problem (huge flat belt cast pulley with uneven center hole). Check to see if the spindle is bent. Jim
Phil, have you recently tightened the rawlbolts and inadvertently warped & twisted the lathe bed? Does the wobble disappear after you true a sacrificial block attached to a faceplate? Do you put too long a tenon or dovetail on the blank for the chuck to center & hold? Does a M900 have a rotating headstock? Diagnosis is usually difficult---treatment often easy. ;) Arch
With the lathe off, rotate the piece with the toolrest up close. Look at the gap - Is there one close approach point or two?
If one, pursue mounting problems.
If two, take a look at a couple of wild ideas.
If two, diametrically opposed, and on the endgrain, what you have is a natural result of releasing the tension of the wood by hollowing it.
What you must do is either go inside to outside and back again when hollowing, realizing that you will be causing substantial risk to the turning as it gets thinner, or use a bowl steady to help maintain circularity until the hollowing is complete.
Wild idea number two, which is suggested by your remark that an unhollowed (unhallowed?) piece wobbles. It could be that you're riding the tool on the piece versus steadying it on the toolrest and letting the wood come to it. What happens here is the tool dives into the face grain and climbs into the end grain. This is often accentuated by sanding with the paper supported on the work, as you can easily sand the face, but end grain only with difficulty.
You mentioned that you used up all your hoarded timber. Are you now turning "green" wood? If turned thin without allowing the wood to try it will warp causing a wobble.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
Axminster have dial tested my headstock bearing and they are within tolerance ending any warranty discussion. Derek, I did try the faceplate adaptor on the chuck, no wood, seemed ok (visually) after re-seating in a couple of different positions, and clearing the recess of any small wood particles The headstock does rotate and whilst I have to be careful with alignment for between centres turning, (+/- a lot)on faceplates/chucks etc. when tightened (not quite broken tight) I can't move it.. Arch, I did check and re-tighten my rawbolts, and all four had relaxed a bit in the short time since having the lathe, and subsequently tried any bit of wood, turned to almost nothing, seems to exhibit the same eccentric (visible) motion. I do tend to make the chuck recess deeper when compared to pro turners bowls at local craft fair/shops etc, to err on the safer side of ignorance I thought. James, I have no way at home of checking the straightness (I think) of the headstock shaft, but would hope that the supplier had done that when I took the motor/headstock assembly in for testing. Jack, the last bowl blanks were "shop bought" from local wood turning supply retailer, "part seasoned" I'm told, they look and feel dry after turning off the wax. George, in two positions relative to the toolrest, 180 degrees apart, so is it me, am I riding the bevel harder than securing the gouge to the tool rest, would that cause this ovality. And I do have some difficulty removing torn grain during final sanding, seems to take forever no matter how little there is of it.
Phil (with thanks to all)
"Derek Hartzell" wrote in message news:n2Rub.20$ snipped-for-privacy@news.uswest.net...
Rather than "ride," try to "guide" the bevel, and you'll begin your sanding in a better state.
I use a flexible shaft powered by a washing machine motor to sand. That way I can rest the handle of the shaft on the toolrest to steady, rather than referencing the disk on the work. Double benefit, really, as I don't have to press, thereby aggravating the natural tendency to sand faster in soft face (or spalt), slower in end grain. Heat is also the enemy in sanding. It hardens and burnishes the surface, and the tears are more obvious by comparison. If you're able to kiss, rather than press the work, you'll have less heat. If you do start to burnish the work when sanding, don't do what seems natural and press harder. Stop, wet the shiny areas to break the hardening, then return after the surface looks dry.
Take a peek at my weird technique, which involves running the gouge with the angle of attack parallel to centerline.
A remote diagnosis is difficult, but if your spindle is within tolerances but you are eccentric, then the problem may be the mating surfaces between your spindle and the faceplate. Mounting the faceplate "true" on the spindle does not come from the threads but from the mating surface on the spindle and the mating surface on the faceplate.
It is easy to check the mating surface on the spindle. If ok, mount the faceplate and check the faceplate for runout. You may have warped or bent your faceplate. It is easier than you think to do this with screws, especially if you use a ratchet for leverage.
thankyou, I do (did use) a power driver to run-in the screws through the stock cast faceplate supplied with the lathe, but for the last couple of bowls I used a new steel faceplate chuck adaptor, and noticed the same level of perceived movement. Even on a small blank, say 4 x 2" I struggle to get it square to the axis of rotation and worse when reversed and chucked for hollowing.
Many stores have double ended morse tapers. When you take your spur center and live center out you can align the two parts. Most lathes don't have adjustments for the angle for the headstock once it is locked down, so once you move the headstock, you have to reset.
I have a double end Morse taper that I used to align the headstock and tailstock on my Nova 3000. I believe that Woodcraft sells them, that is where I purchased mine several years ago. It allows you to return the headstock to align with the tailstock before locking it down.
A close way however, is to put centers in both tailstock and headstock and eyeball the alignment. Not as accurate as the double ended Morse Taper, but generally close enough.
I have a double end Morse taper that I used to align the headstock and tailstock on my Nova 3000. I believe that Woodcraft sells them, that is where I purchased mine several years ago. It allows you to return the headstock to align with the tailstock before locking it down.
A close way however, is to put centers in both tailstock and headstock and eyeball the alignment. Not as accurate as the double ended Morse Taper, but generally close enough.
Dr. Deb, if you are using the lathe to turn between centers (legs?) it won't matter if the tail stock and the headstock don't line up. The turning will still be fine.
If, however, you are using the tailstock to 'steady' a piece held either in a chuck or on a face plate, simply turn the lathe on (slow), slide the tailstock up until the point nearly touches the wood, then screw it forward until it scores a circle on the end of the wood. Stop the lathe, then move the tailstock (assuming there is enough movement, in the right direction) so the point is on the center of the circle you scribed earlier.
Now, assume the point is too high. You can either shim up the headstock, or file down the bearing points on the tailstock.
If the point is too low you can file down the bearing points on the headstock assembly. (Bearing points are where the head/tail stock touch the ways of the lathe).
Before doing all this, make sure that the spindle is parallel to the ways. This procedure utilizes the tailstock center point as a fixed reference point. First, chuck up a thin (3/4") disc of wood, bring up the tail stock until the point just touches the disc, then rotate the spindle. Measure the difference in height from the center of the scribed circle to the center of the tailstock point. Should only be a few thousands, or maybe 1/16" at most. Then put a longer cylinder of wood into the chuck. This cylinder should be 1' long or longer. Scribe a circle on the end of this cylinder. Measure the difference in height from the tailstock center to the center of the scribed circle, just as you did close to the spindle. If the spindle is parallel to the ways, this difference will be the same. If not, adjust with shims or filing on the contact points of the headstock until these measurements are the same.
Ideally, the scribed circle(s) should be points, meaning everything is lined up and in adjustment. If not, you can figure out what you have to do to get the scribed circle to end up as points.
If the tailstock center point ends up either on the left or the right of the scribed circle, but is on the same elevation as the center of the circle, on both scribed circles (disc & cylinder), then the spindle is parallel to the ways and all your adjustment needs to be to the tailstock. Figure out which way you need to move (c*ck) the tailstock, and if it doesn't move enough, file the approporiate side of the metal that sticks down between the ways. This will make the tailstock sloppy, but if you have to, say, pull the tail stock toward you to make it align, then remember to pull it toward you each time and you will be okay.
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