Power sanding

[Democritus]

Hi Guys,
When power sanding (using either a drill or inertia sander) , what is the optimum size of sanding disc to use? I have used the standard 50mm, but it seems to leave marks around the inside of bowls. Should I use a bigger disc? Or is there anything els I should be doing?
D.

 

[Stigmorgan]

I use the same method and don't have any issues, how hard are you pressing against the bowl? If you're using sandpaper perhaps some of the grit is coming off and getting caught up in the next grit.

 

[paulm]

Are the marks being caused by the sanding or are they there before sanding and not being removed by the sanding ?

Pics may help too.

 

[Phil Pascoe]

It helps to have a soft pad between the abrasive and the arbor and it can help to use a square of abrasive instead of a disc - the corners flex and don't dig in.

 

[Democritus]

Thanks, guys.
Paulm, the marks appear during the sanding, rather than being present before. They are circumferential, and I have wondered if it’s the edge of a small sanding disc that is doing it, in spite of me keeping the sander moving. That’s why I asked if a larger disc is better.
Phil, i’m not sure what you mean by having a soft pad between the abrasive and the arbor. I use Simon Holland sanding discs carriers which are soft, with the usual Velcro to take the abrasive discs.
Stig, I have tried varying the pressure, but with varying results. I suppose that’s the result of hardness differences between wood species.
Richard Raffan recommends ‘firm’ pressure when power sanding, but that begs the question ‘ how firm is firm?’
I suppose i’ll have to keep trying!
Best wishes

D.

 

[Phil Pascoe]

A Simon Hope arbor.

 

[Democritus]

Cheers, Phil. Where do the larger pads come from? I have the Simon Hope sanding kit, but it doesn’t contain any of the fat pads in your photographs.
I have always sanded by hand, often with the lathe stationary to deal with torn end grain, but I’ve read that power sanding gets the best results ( and is quicker), hence my trying it.
D.

 

[Phil Pascoe]

They came with the sets, I've just checked the smaller set as well and there are a couple in each.

https://hopewoodturning.co.uk/sanding-items/hope-pro-sander/247/hope-soft-sanding-pads.?c=32

 

[paulm]

I doubt the diameter of the pads are the issue unless you are sanding small bowls with a deep/tight curve where a smaller pad would allow the abrasive to follow the tighter curves better with less edge digging in ?

 

[Democritus]

Thanks, Phil. I’ll get some.
Paulm, I have been using the smaller pads for everything, as I don’t, yet, have larger.
D.

 

[Phil Pascoe]

I doubt the diameter of the pads are the issue unless you are sanding small bowls with a deep/tight curve where a smaller pad would allow the abrasive to follow the tighter curves better with less edge digging in ?

That's why I got a set of 36mm arbors. A 36mm arbor with a soft pad will get in just about anywhere.

 

[Robbo3]

You haven't mentioned lathe speed. When sanding by hand it is recommended to turn the speed down to 500 RPM or slower but with rotary sanders the speed can be left at whatever was used for the final cut. For general spindle work Simon Hope says he will often turn the speed up to 2000 RPM - which would probably be my final cut speed anyway.

 

[Democritus]

Cheers, everyone.
I’ve ordered some of the soft pads from Simon Hope. When they arrive I’ll give them a go, and report back.
D.

 

[Democritus]

Hi Guys,
I got the soft pads ( 50mm) from Simon Hope, and they really help with power sanding. I also sent for a 36mm arbor and some 36mm soft pads as Phil recommended . When I came to try them I realised I didn’t have any 36mm sanding discs (doh), so I will have to get some of them, unless anyone knows a way of cutting 50mm discs down
D.

 

[Phil Pascoe]

Discs of exactly the same size as the arbor seem more likely to scar than oversized discs. Some of the fleece backed very flexible abrasives work very well used in squares - the corners just lift off the work. This is handy when working into curves. I'm going to cut some c40mm discs from larger discs of Cubitron, which doesn't appear to be available in sheet form.

 

[Democritus]

Cheers, Phil. Thanks for your helpful advice.
D.