Trimming the edge true on spinning projects

[Fe-Wood]

So I thought I would do a little practice spinning work today between cutting loads of firewood....
I have finally come to the place where I can make it work. Now I need to fine tune some of the other components of spinning.
After setting the base and forming the cone I do a trim to even and clean up the edge and I get chatter. I have tried lub, change of angle, change of speed, working on the high and low sides of the arch, more positive pressure and changing the bevel angle on the cutter. The cutter is a HSS 1/4" lathe cutter mounted in a 5/8"Ø bar with a maple handle, total length is about 30". I get chatter like no tomorrow (sometimes). What am I doing wrong?

[Mainely,Bob]

Most chatter can be traced to lack of support for either the work or the tool.One or the other of them are being pushed and/or flexing out of the cut.
As I`m sure you have realized support is one of the keys to successful metal spinning.If the metal is not supported by either the form or a backer stick then it wants to distort and buckle.The same forces are at work when trimming.
When trimming early on(that uneven edge makes you nervous doesn`t it)you are creating a line where one end is the last point of solid contact with the form and the other is the cutting tool.When that line is too long the metal flexes and the cut chatters.I try to make that line as short as possible by using my backer as close to the cut as I can and still be safe.
Quick question,how long are the handles on your tools?

[Fe-Wood]

Thanks Bob-
I start off with a piece of cold roll about 18" long and set that into the handle about 4-5". I can't remember exactly but I think the wood handle is 22" long for a combined length of 36". The diameter of the handle is around 1 3/4".

I have noticed that if I apply cutting pressure into the strongest line (area of the least flex) of the spun form its better and sometimes it cuts like it should. More often than not though, I get chatter.

[Mainely,Bob]

The reason I asked about the handles is that some folks make them too short.The longer the better within reason.
Better control comes from having a 3 point contact at all times.You need to be contacting the rest(both pin and crossbar) have a firm but relaxed grip(like forging with a hand hammer)and good contact between the handle and your body(upper thigh,hip or slightly above).
You probably already know this but a smooth surface and flowing curve come from pushing with your body not your hands and arms alone.
Even on smaller or detail tools having a longer handle adds momentum and helps smooth out your movement and make things flow instead of jerk.it also helps to dampen vibration.
It also helps to keep moving the rest as close to the work as you can.Think about adjusting the rest between pushes,make leverage work for you instead of against.

My apologies if I`m stating stuff you already know.

[HWooldridge]

Bob hit many of the salient points but speed of the workpiece also affects chatter. Try reducing the RPM's and see if it gets worse or better. Often, an increase of speed will fix a chatter issue but it's often hard to clean up a cut where it already exists - especially in a flexible setup. A thinner edge on the cutting tool may also help - big fat edges with lots of surface contact often chatter if the feed rate is not high enough.

[mike-hr]

I made a freehand trimming bar that fits in my scissor spinning setup that uses a 3/8 inch toolbit. I ground it to a simple vee shape, like a threading bit. I wait until the piece is just about finished, I think you said the same thing there, the bell shape adds some strength to the piece. What i had to get over is, These pieces I'm working on have a 8-12 inch O.D. when done, and even though I'm just cutting through a piece of sheet metal, the tool bit thinks its cutting on a 10 in shaft..I slowed the rpm down a lot, compared to the spinning process, and am doing okay now.
FE, are you going to the hammer-in in Weaverville in March? It would be plenty fun to bring our mistakes, and compare & contrast...
mike

[Fe-Wood]

All good stuff thanks to all of you

Bob-
I measured my trim tool today its 32" total. I agree with all you said and do most of it. Nice to have corroboration.... One question- how close do you put the tool rest? Mine is anywhere from 3" to 6" away depending on what set up I'm doing. I may end up making a scissor tool trimmer. One issue though is my lathe is only 3/4HP and I stall it often when trimming.

HWooldridge-
Speed may be the issue and lack of power. I just occurred to me... Has anyone tried shaping the tool to cut on the bias? Like you do with a file? Hmmm...

mike-hr-
Ya, I go as slow as the lathe can... about (an unverified) 360RPM. Weaverville, Yup! Thanks for reminding me!!! That would be fun and informative (I got lots of mistakes too). Where are you located? I tried to order "draw quality" steel today "nope, never heard of it, I've got cold roll sheet" Any suggestions?

My trim tool is cut in a "V" shape too- what relief angle do you all use? I'm using about 2 degrees. I used a steeper angle (about 10 degrees) when I started but found that to catch to easily.

[Mainely,Bob]

My cut off tool is also shaped like a thread cutting bit.You can always use one side or the other(stay close to the tip and center)to present a wider cutting edge if needed.
As far as relief angle goes.I use the least I can get away with as I like to use 1 bit rather than a bit for each different metal if I can keep from it.Too steep and it it gets dragged in on things like copper.Too shallow and it rubs and maybe work hardens what you`re trying to cut.I`m not doing production work so I aim for scraping and control rather than aggressive cutting and speed.If the relief angle seems right but the tool is too thick to get in where you want(depending on where on the arc you`re working)then grind away part of the heel for clearance,All you really need is a small bevel and enough metal below to support the cutting edge safely.
Whatever metal you`re spinning needs to be as soft as you can get it to start.You crank stress into it and harden it by working it.Cold rolled has already been somewhat work hardened by the rolling process.If it were me I`d anneal to to soft,pickle it,and prep it as needed for finish B4 spinning or just buy soft steel to begin with.Can you get annealed and surfaced stock?It`d be worth it to buy even a small piece from a knowledgable online supplier so you`d be able to work it and know what to shoot for from start and when to pull it and anneal back to soft.

The tool rest.The best answer I can give you is as close as you can get it(especially for trimming)and still have room to get the tools in comfortably thru the entire planned push or operation.If in doubt practice with the lathe off and make adjustments till it goes smoothly THEN hit the button.
Just starting out it may be worth your while to also stop the lathe if you`re unsure or when things go wrong and look at what`s happening.Present the tool while spinning the lathe by hand,many times you can still see what`s happening at that low speed.That trimming tool should still pull a chip at hand speed.If it doesn`t then maybe it`s not as sharp as to could be and that`s contributing to the problem.

[mike-hr]

I'm using 55 gallon drum lids. I was told (can't verify) that drum lids are a lower carbon steel. A buddy gave me a stack of them, they cut real nice on the Beverly shear. I'm having better luck with them, than with store bought sheet metal.
On a slightly tangental note, does anyone know how or a youtube link to 'Hem' the edge? Don't know if that's the correct term, I've seen examples where the last 1/8 inch or so is folded/spun back onto the piece, leaving a more finished look.
FE, look for us downstairs at Weaverville. McraigL and I are doing a workshop on chisels for making animal heads to compliment the Darryl Nelson demo. We have a portable shelter made from lodgepole pine poles, with a green canvas roof.

[Fe-Wood]

Here are a couple links for two different methods of rolling the edge. I haven't found any for hemming. If you roll a very small edge and flatten it before the roll is fully formed that turns into a one fold hem. Mine have been very prone to wrinkle.