Inflatable Contour Drum Sander Question

[mr.d]

Anyone have an idea on how stiff or how much this sanding drum will bend or contour with minimal air pressure? I'm making spheres that are baseball size and looking for a little more reliable method for sanding off the little nib or tenon. I use either a flapper wheel or small sanding sleeve in my rotary tool now with good results but if I'm not paying attention........sometimes I get an oops and create a little flat spot. Can you push a baseball sized object into the drum and have it conform to that shape? I've watched a few videos that show it doing table legs but I can't tell how much the drum is actually conforming to the parts shape. Thanks in advance

[reible]

Hi,

I'd say it's not going to work. Too stiff.

If you have a shopsmith belt sander then you might try the back of it. I've used that before for some rounded shapes and it did a pretty good job. Just make sure you have a fine grit belt on, the finer the better as they cut slower. If you have the PTWFE book I think they show it in there.

Ed

[everettdavis]

Take a piece of something like a sand blast stencil mat etc. and cut an opening for the nib to protrude through.

The hole will give you a sanding shield to prevent getting into the ball, by contacting the protecting material when you are done.

This will help prevent that flat spot. I once used a leather glove that had a hole in the palm to do something similar once.

You can use a piece of leather or any suitable material with an appropriately sized hole. The old glove gave me a gripping surface to hold the ball I was working on, but you get the idea.

Everett

[JPG]

A sharp knife or chisel comes to mind.

[ChrisNeilan]

A sharp knife or chisel comes to mind.

I use my skew, when I remember to grab it! The problem is if your not very careful you run the risk of snapping the nub off, rather than cutting it, sometimes pulling fibers out of where the nub was leaving a small hole. That is a PITA to sand out!

[mr.d]

Thanks for the replies. I think I'll try each one of the suggestions to see if they work any better than what I'm currently doing. Ed, I do have and have tried the belt sander (didn't like results) but never thought of using the backside. Looked it up in the PTWFE and sure enough, a pic of a somewhat similar application. Thanks for the heads up. BTW, I've also tried the strip sander but the platen keeps the belt to straight. Was thinking of trying it without the platen to see if I can get any contour in the belt.....just haven't tried it yet.

[JPG]

A sharp knife or chisel comes to mind.

I use my skew, when I remember to grab it! The problem is if your not very careful you run the risk of snapping the nub off, rather than cutting it, sometimes pulling fibers out of where the nub was leaving a small hole. That is a PITA to sand out!

Slice, not pry!

[everettdavis]

This video shows you how to turn the ball and not leave a nib at all...

He isn't using a Shopsmith, but this would work on one just fine.

https://www.youtube.com/watch?v=3lConTQ-cUw

Everett

[mr.d]

Everett,

I've watched Alan's video numerous times and have done it his way a few times, some more successful than others. I usually do pretty good on the right half of the sphere but getting the left side perfect is always a challenge. Don't know if it's a left brain/right brain thing but I just never seems to get that arc on the left side to match up.

I have a sphere jig that I got on the cheap but my preferred method currently is using the Berger Sphere Caliper. Here's a link to the demohttps://www.youtube.com/watch?v=R4s5LziiS08

This is a pretty quick method to make a sphere without a lot of guesswork as to how much more to take off in any one place and leaves a nice surface finish. At the end of the video he shows a collet that grabs the sphere in his chuck to get the nub off. It works well at holding the piece but leaves a mark in the piece that needs to get sanded away (not good). The size of the nub shown is about the size I get so that's why I thought finding a way to get a little contour to some type of drum or belt sander might be a quick alternative. I know there's a number of different ways to make spheres but for me, this method seems to work best for me in not having to chase one size of the sphere and then the other just to get something round.
Dave

[rpd]

Everett,

I've watched Alan's video numerous times and have done it his way a few times, some more successful than others. I usually do pretty good on the right half of the sphere but getting the left side perfect is always a challenge. Don't know if it's a left brain/right brain thing but I just never seems to get that arc on the left side to match up.
Dave

A way around that would be to cut the right side and then turn the sphere 180 (left side become right side). Then cut the "left" (now right) side to match.