Disc Sander speed

[tablesawtom]

What is a good RPM for a 12 inch disc sander? I know a lot of sanders are direct drive to a motor. I have never checked but I assume they are of the 1725 RPN verity. I know that Shop Smith has a a variable speed system and there is a range in that system. 

More information, I have a 9 inch disc sander attached to my 1 x42 belt sander and and one attached to my 4 x 36 sander And since they are attached directly to a motor, the rime speed would be a lot slower than the rime speed of a 12 inch disk. I also have a 12 inch that the disc is attach directly to the motor. It is reversible and I like that feature. But it is a pain to have to pull the entire table to change the paper ( cloth ) discs. Also for me the tables are very small and I find it hard to support larger pieces

I hadn't planned on posting this at the present, so I don't have the exact information but, I have a reversible motor off from an old Delta shaper. It is a small motor and I am guessing it is a 3450 motor 1 HP or smaller. I have a 2 inch pully on the shaft that supports the Discs and I am looking for an optional speed so I can get pullies for the build.

I can go to my machinery Hand Book to calculate the pully sizes I need. 

But if someone knows the optional speed  and pully sizes it would be greatly appreciated.

My shaft is a precision ground 5/8 shaft and it fits the bearings perfectly but the Shop Smith discs I purchased will not go on , size for size doesn't work. I will take it to work tomorrow and emery paper the shaft diameter down so the disc will go on. Then I will post pictures of what I have to date and get the motor information also.

Thanks for your help in advance.

Tom

[tablesawtom]

I had time to go over to the shop after I posted. The motor is a 3/4 HP 1725 RPM motor. and I checked my 12 inch disc sander and it is a 1725 RPM motor. 

I guess I have been thinking about this build for a couple of years and have been collecting parts. It seems I have been here before because I have a 2 inch pully already on the motor and a 2 inch pully on the shaft so I am at 1725 for a speed. Which is the same speed as my commercially made disc sander runs at. It is called getting back to an unfinished project. I am sure that none of you have any of those.

I have some other engineering ( research and development ) things going on so I will post some pictures as when I get my shaft and disc to fit tomorrow. 

Who knows maybe I will give someone else an idea.

Tom

[MarkSingleton]

" . .  It is called getting back to an unfinished project. I am sure that none of you have any of those. . . "


Tom

   I wish that were the case.  I can glance around my shop, or garden/yard and find dozens!


   

[DieselDennis]

You may want to consider surface feet per minute speed as well as RPM. Sounds like 1725 is the standard RPM for most direct drive sanding discs, but keep in mind as you move from the center of the disc outward, the speed of the sandpaper passing across the wood is going to increase significantly.

Nothing wrong with your plan, just wanted you to keep this in mind.

[tablesawtom]

You may want to consider surface feet per minute speed as well as RPM.  Sounds like 1725 is the standard RPM for most direct drive sanding discs, but keep in mind as you move from the center of the disc outward, the speed of the sandpaper passing across the wood is going to increase significantly. 

Nothing wrong with your plan, just wanted you to keep this in mind.

Yes I know this,  but as far as a disc sander goes there is nothing anyone can do about it It is called constant surface speed. On CNC lathes the RPM will go up as the diameter is reduced but the cutting speed remains constant. And visa versa. I was working on a manual lathe and I had to stop and change RPMs once per part.

Tom

[tablesawtom]

I have a 3/4 HP reversible motor. I like having reverse, Lets say you want to do a 1 inch radius on each end of the board. One doesn't have to layout the radius on one side and then turn it around and layout other end. In this case one could just switch discs. But I am leaning on each disc having a different grit.

I got it together for the first time this afternoon and the spacing was 8 or 9 inches apart. I think that it is a little to wide so I will cut 3/4 of an inch on both ends and then recut the whistle notchs.

   

Then I checked for center line height to base to see where it came to. The table is about 7/8THS below the center line on the purchased disc sander I have and this new one is about 1 1/8th . From what I can see the 1/4 inch won't make much if any difference to the sanding operation.

   

   

 99% of all sanding that I do is at 90% so I am not planning on making the table to be able to be put at an angle. I am not sure if I will keep the table as it is or turn it 90 %. I have some other things to consider also. Again I am just in the research and development stage right now. The top is Corian.

Tom

[Hank Knight]

I've been thinking about something like that. You're looks like it's going to be very nice. What are your discs? Where did you get them?

[tablesawtom]

I've been thinking about something like that. You're looks like it's going to be very nice. What are your discs? Where did you get them?

My discs are from Shop Smith and I bought them over time on eBay. The bearings are from Amazon and the pulleys I got locally. I aske at work for the shaft material and that is where I started. I had nothing to go on so now I an planning on cutting 3/4 of an inch off from each end.

Tom

[Hank Knight]

My discs are from Shop Smith and I bought them over time on eBay. The bearings are from Amazon and the pulleys I got locally. I aske at work for the shaft material and that is where I started. I had nothing to go on so now I an planning on cutting 3/4 of an inch off from each end.

Tom

Thanks! I thought about Shop Smith discs, but I've never gotten around to looking for them. Time to start, I guess.

Hank