Old round punches - yard sale finds - need some TLC

[Sprocket]

17 hours ago, dikman said:

If you have an ac motor belt sander (most likely) then no, a dimmer switch or rheostat will not work. There is no easy way to control such a motor. Variable speed grinders/belt sanders generally use a 3-phase motor with a Variable Frequency Device (VFD) used to control the speed. These can be run off the single phase household supply.

To clarify:

My machine is 120V 1phase 60hz, 1200W - a bench top 1x30 sander from Harbor Freight - not an expensive unit (approx. $40).  Closer to a vintage sewing machine than not.  A rheostat controller can throttle the current flow and moderate the motor speed much like a vintage sewing machine - for about $30 shipped.  No lighting dimmer switches need apply - not rated for the job - but a motor controller appropriately rated.

Compared to an industrial machine at 3phase of any voltage utilizing an electronic VFD - a completely separate piece of equipment there.  That's more of a professional knife maker or metal fabrication shop item.

Northmount - following the cone, yes - not true horz/vert but a general orientation of the part to the belt.

Oltoot - Thank you for reminding me about temper and heat.

The experiment continues...

Thank you All for your input. appreciated.

[bruce johnson]

On 6/3/2024 at 6:51 AM, Sprocket said:

Thank you again Bruce - I'll PM if I get stuck. In the meantime...

I was thinking of adding a pedal control like a sewing machine - or some other rheostat controller to control speeds on the belt sander. - I wonder if a dimmer switch would work?

Once I get the speeds managed - do you hold the part horizontal or vertical to the belt?  I can see creating a "grain" by holding the part vertical - in line with belt travel vs horizontal/perpendicular to belt travel.

Can you expand on keeping the part rotating?  I get the concept but do you use a jig, etc. to keep the part moving?  Or is it more of a feel with just your hands?

After that, it's just going through the grits to get a polished face?  What about squaring up the mouth?  If you look close you can see the irregularities there.

Am I overthinking this?  I do that - often...

First off if the edges are irregular you need to square that up. Open side down on abrasive paper until you get a flat edge all the way around. 
    Then when you hit the edge to the belt you need to already be rotating the punch in your hand. Same for removing it from contact with the belt. My angle is slightly higher than the coning of the punch to make a slight secondary bevel. Anytime you leave the punch sitting against the belt without rotating it you can create a flat spot at worst and thin spot at almost worst. Watch how the edge develops. Magnification is your friend to see closeup and get an even edge thickness. (Optiviser with a #5 plate is my usual choice for punches, #10 for finer work) As the flat edge gets thinner and thinner you should be going to finer and finer grits to refine the edge and remove grit marks from the outside edge. The final abrasive should complete the bevel and make a fine burr on the inside of the edge. I use a diamond file to remove that burr. I polish on a sisal wheel with black and then green compound, sometimes go on to purple. Wipe the burr off the inside again and polish some more until the burr fragments are gone. 
     

[Sprocket]

Thank you Bruce - this should be enough for me to be dangerous.  The $$ I'll spend on belts and supplies will probably afford me at least one new punch but hopefully I'll develop a new skill - or at least rule it out.

[dikman]

On 6/5/2024 at 2:33 AM, Sprocket said:

To clarify:

My machine is 120V 1phase 60hz, 1200W - a bench top 1x30 sander from Harbor Freight - not an expensive unit (approx. $40).  Closer to a vintage sewing machine than not.  A rheostat controller can throttle the current flow and moderate the motor speed much like a vintage sewing machine - for about $30 shipped.  No lighting dimmer switches need apply - not rated for the job - but a motor controller appropriately rated.

 

Have a close look at the motor, if it uses brushes then yes, a simple speed controller should work (although I would suggest an electronic controller rather than a simple rheostat), if the motor doesn't have brushes then it is an induction motor and the controller WILL NOT work.

Vintage sewing machines used brush-type motors to allow for rudimentary speed control.

[Sprocket]

13 hours ago, dikman said:

Have a close look at the motor, if it uses brushes then yes, a simple speed controller should work (although I would suggest an electronic controller rather than a simple rheostat), if the motor doesn't have brushes then it is an induction motor and the controller WILL NOT work.

Vintage sewing machines used brush-type motors to allow for rudimentary speed control.

Thank you for that info - if it's a brushless motor, would there be a module or other indicator?  I'm not exactly sure I'll be able to get into the motor that far - I may have to do some disassembly of the machine to verify.

I'll certainly look at an electronic controller.

[dikman]

If it uses brushes then there should hopefully be some sort of screw fitting where the brushes are mounted, there will be two on opposite sides of the motor housing.

[Chef niloc]

Another way if you don’t have the power tools is the “mousepad sandpaper sharpening technique” there’s tons of articles on it if you Google it but basically it’s just what it sounds like.Aautomotive wet/ dry sandpaper ( 500, 800, 1000 grit is what I use) on top of a somewhat forgiving service. Rubber cutting mat or a newspaper/ magazine I’ve heard works. I find it best to spray It was glass cleaner ( the aerosol one) as opposed to just water..