Laser Guided Hollowers

[Mark Mandell]

I'm currently putting the finishing touches on the captured -frame hollowing rig I designed and built. It's an adaptation of the Jamieson-style rigs.

I'm getting kind of a lot of vibration at the laser with certain cuts, and am looking to reduce that condition. My holder boom is made from 1/2" EMT (5/8"ID thinwall) that has been filled with 1-part urethane foam.

For anyone who uses this kind of set up, I'd like to know

1. If you've tried to use a counterweight at the opposite end of the boom to balance the holder,

2. If so, whether it helps the vibration, and

3. If so, how much weight you used?

Thanks

mm

 

[Frank Alvarez]

I am certainly no expert , but the guys who showed us how to build these at our club use heavy tubing. I made one with black plumbing pipe. I haven't seen one with a counter weight
But I have seen a lathe weight on a pedestal atached to the bed to cut down on vibration, so the same should work . If your tubing wasn't filled , you could fill it with sand ,or even better lead shot, which should also work. The other thing that might work is to extend the tubing more and if the problem still ,persists add the weight there.
I guess your question was really how much weight? I think that would depend on the dimensions of your set up. For that type of question ,I usually attach some temporary device either hanging or strapped on ( bucket? bottle?box?) and start adding weight(water, sand , lead) until it seems to cure the problem or becomes obvious that it's not going to help.

 

[Mark Mandell]

Thanks, Frank.

My upright post is heavy guage steel, but the boom is light. The foam fill acts to deaden the small vibrations, and I was told to keep the boom and laser as light as possible to avoid the weight stress on the parts. What I may do is extend the boom backward and then, as you suggest, hang a cup or something to add or take away balancing weight.

 

[Steve Worcester]

What size boring bar is this and what is your expectation as far as how deep of a form you want to work with?

 

[Mark Mandell]

Hi Steve,

My rig is set up to take boring bar stock from 3/8 to 1" with adapters. I can, of course, go above that with a machined end on the bar, but I don't anticipate doing so. My 1" bar, sans cutter, is 24", to give an effective depth of about 21". Right now I'm using Jordan and Pencil 3/4" shaped bars for the primary work, and several 1/2" and 3/8" tools for neck/rim/close-to-opening cuts.

With a sharp cutter, the vibration is almost nil for finish cuts on the vessel walls, but hogging out from the center and doing the jar bottom gets the spot dancing pretty well.

Thanks

m

 

[Vernon Oberle]

Vibration

I find I get the vibration on heavy cuts while hogging out the middle. I just don't put the laser on until I get ready to make the final cuts where I'm taking small cuts with each pass. I put the foam in my bar and have tried other heavier bars but when you make a heavy cut they all seem to vibrate.

Vernon

 

[Ed_McDonnell]

21 inches over the rest without serious vibration seems like a lot to ask of a 1" bar.

Ed

 

[Mark Mandell]

21 inches over the rest without serious vibration seems like a lot to ask of a 1" bar.

Ed

Can but try, Ed.

Actually, I doubt I'll get much over 18". Not planning to challenge Mr. Tsiris anytime soon.

m

 

[Tony Reynolds]

Mark,
I made my laser guide by using 2 uprights. One at the front of the capture and one at the back end. The laser holding bar is made from telescoping aluminum tubing about 1" diameter and 7/8" on the inside piece. I slit the 1" and use a hose clamp to trombone the inside piece so I can adjust the distance and angle of the laser. I'm using the Kelton capture device but I'm sure this would work on others, No problem with vibration.

 

[Steve Worcester]

The tricky part is the base where it mounts to the captive bar. I have three setups, a 3/8" a 3/4" and a 1". I have hollowed to 24" on the latter.

The bar I use for the laser is 3/4" diameter, cold rolled steel tubing. Tubing is better at reducing vibrations than bar stock. As long as it has some length hanging over the back end (at the length adjustment), you will also get a little more absorption there. The key is to dampen the vibration. Since the lase if used mostly for just "sighting" the wall thickness and the final cuts, i don't pay much attention to the vibrations otherwise. What you want to do anyway is to minimize the vibration during hollowing so there isn't as much transferred up to the laser anyway. Most of that can be dampened at the hollowing rig, but you trade off the ease of movement with tightening the gap at the captive rig. Having an adjustable captive rig helps alot, as well as the cutter head. The traditional head, like on a Jamison, with the swivel head and the 3/8" bar, is the worst for vibration. The reason is that you have the cutter attached to the head, attached to the bar. On some scale it acts as a chatter tool. Minimize the amount of the 3/8" bar and you will cut down on vibration.

This is one reason I use the McNaugton cutter where I can.The thicker the cutting head, the better at absorbing the vibration. I have also made a swivel tip cutter that puts the swivel on a cut out at the head and no 3/8" bar. This limits the swing of the cut, but also the vibration.

To get back to the laser, I drill a hole in the end of the 3/4" tube, perpendicular to the bar, the diameter of the laser, pretty close to the end of the bar. I then put a plug in the end to jam the laser in there. The upright is a 3/4" black pipe "tee" that has a set screw in it to lock the length of the overhang. The other important pint is to keep the laser vertical so that you don't have parallax issues for the laser that would give you a false edge (wall thickness).

If I remember, I will snap some picks later.

 

[David Somers]

The tricky part is the base where it mounts to the captive bar. I have three setups, a 3/8" a 3/4" and a 1". I have hollowed to 24" on the latter.

The bar I use for the laser is 3/4" diameter, cold rolled steel tubing. Tubing is better at reducing vibrations than bar stock. As long as it has some length hanging over the back end (at the length adjustment), you will also get a little more absorption there. The key is to dampen the vibration.

Steve,

One of our local turners has found that filling the hollow tubing with sand helps to dampen vibration a great deal. He is working on a larger scale than this (turning vases 3 to 4 feet tall), but I would suspect it would work just as well on this scale. Easy enough to try.

 

[Mark Mandell]

Thanks for all the responses. I'm picking up a longer piece of EMT this afternoon.

M