Electronics > Projects, Designs, and Technical Stuff
Speed modification
davelectronic:
Yes final finish could be lapped, it is time consuming though. In an ideal world I'd have put them in a four jaw chuck and face them off.
Thanks for the input.
mikerj:
Use a hand file to remove the saw cut marks before moving to wet and dry paper. Chalk the file to discourage aluminium sticking in the teeth and draw file (i.e. hold both ends of the file and apply is sideways across the work) to get the best finish.
Sorry if this is frustrating, I know this isn't addressing you original question but given the application I just don't think a belt sander is good solution.
rstofer:
--- Quote from: davelectronic on October 09, 2019, 07:32:33 pm ---Hello out there to the community.
Think I've chosen the correct section to post this in.
I'm trying to find a way to slow down a hand held belt sander. I think it's a universal series motor of 800 watts, on the tool handle is a small control wheel that goes from 1 - 6 for speed. Although 1 on the wheel is reasonably slow, I could do with Slowing the belt down a little more. It's for standing flat some heatsinks I have, these had a raised portion which I cut off. So need to flat the face off. I don't have access to a lathe unfortunately, Slowing the sanding belt speed will give me better control for final finished surface of these heatsinks.
--- End quote ---
Google for "universal motor speed control" and there are hundreds of projects but you can also buy a speed control for < $20.
https://www.harborfreight.com/router-speed-control-43060.html
davelectronic:
Thanks for the tips, for now I'm going to project box that boost converter. It seemed to cope with it fairly well, i think it got up to about 180 watts. And i was using serious pressure at times. But sure will look for universal motor speed controller. With a file i find it hard to keep a real flat profile on such a large flat area, its ok with file until you grt close, with about 1mm ish. Carrying on with a file zfter thst risks uneven material removal.
But thanks again for all your tips and ideas.
Nominal Animal:
If I were to do more than a couple of more of those heatsink mods, I would probably construct a horizontal disc sander, from wood/plywood, a large lazy susan bearing, a ~100 RPM 12V geared DC motor, and an adjustable DC power source.
Typical sheets of sandpaper are about 230mm on the shorter edge here, so I'd make the rotating square 230×230mm in size. I'd get a meter long piece of glue board (solid wood, glued together; very flat) 250mm wide. For paper holders, I'd use aluminium L profile I already have, with a bead of silicone on the inside for grip, bolted to the side of the rotating board (using thumb screws or something, for changing the sand paper easier). I've access to Ikea, so I'd get a set of four 300×300mm mirror tiles for 7€. The 6" lazy susan bearing I'd get from eBay (like this 6" one), and the motor from Banggood (like this or the 110 RPM here; a 6mm flange is also useful).
Here's an OpenSCAD sketch:
--- Code: ---module Lprofile(a,b,t,length=170,d=4) {
difference() {
cube([a,length,b], center=true);
translate([t,0,-t]) cube([a-t,length+2,b-t], center=true);
translate([1-a/2,a-length/2,-b/5]) rotate([0,90,0]) cylinder(h=3, r=d/2, center=true); // Bolt hole
translate([1-a/2,length/2-a,-b/5]) rotate([0,90,0]) cylinder(h=3, r=d/2, center=true); // Bolt hole
}
}
rotate([0,0,$t*360]) {
color([0.7,0.6,0.3]) translate([0,0,78]) cube([230,230,18], center=true); // Rotating 230x230x18mm base
color([0.9,0.9,0.9]) translate([0,0,89]) cube([230,230,4], center=true); // 230x230x4mm mirror
// Paper brackets out of L profile:
color([0.3,0.5,0.4]) translate([-107,0,84]) rotate([0,0,0]) Lprofile(20,20,1,170);
color([0.3,0.5,0.4]) translate([107,0,84]) rotate([0,0,180]) Lprofile(20,20,1,170);
color([0.3,0.5,0.4]) translate([0,-107,84]) rotate([0,0,90]) Lprofile(20,20,1,170);
color([0.3,0.5,0.4]) translate([0,107,84]) rotate([0,0,-90]) Lprofile(20,20,1,170);
}
// Static base
color([0.5,0.4,0.3]) difference() {
translate([-30,0,50]) cube([290,230,18], center=true);
translate([0,0,50]) cylinder(h=20,r=6,center=true);
}
// Supports and hand guard
color([0.6,0.5,0.4]) translate([-184,0,50]) cube([18,230,100], center=true);
color([0.6,0.5,0.4]) translate([124,0,30]) cube([18,230,60], center=true);
color([0.7,0.6,0.5]) translate([-153,0,109]) cube([100,230,18], center=true);
// Motor
color([0.4,0.5,0.6]) union() {
translate([0,0,60]) cylinder(h=40,r=3,center=true);
translate([-10,0,27]) cube([43,32,28],center=true);
translate([-50,0,27]) rotate([0,90,0]) cylinder(h=40,r=13,center=true);
}
--- End code ---
Save the above as sander.scad, and open it in OpenSCAD. I did not include the lazy susan bearing in the model. Press F5 to compile and display it. Enable animation (View > Animate). Set Steps: to 2/3 of FPS, to see how 100 RPM looks in real life. My laptop can do about 25 FPS in real time, so FPS:25 and Steps:15 is pretty realistic.
EDITED: Aw crap, the gearbox would not survive many abrupt starts and stops. The momentum in the plates is so high it'd strip the gears. Instead, a friction drive with a soft rubber wheel (say Tamiya 70192 or similar, or just a rubber O-ring on top of suitable wheel) makes a lot more sense. A 30mm diameter wheel making a 220mm diameter circle makes a ratio of about 1:7.33, so something like 600-800 RPM for such a smaller wheel should work (perhaps something like this).
So, ignore the motor part in this post; that needs further thinking.
It is unsafe as heck, and I've no idea whether it'd work in practice; I'm only saying that is what I would try to build, if I needed machine help in sanding heatsinks.
Knowing what I know now, I'd probably sand the surfaces down to 160 or 240 grit, no further. I would use another mirror as a reference surface, using some ink (like metrologists use on surface plates, when checking if something is flat or not), to check the flatness of the results.
The attachments contain screenshots from OpenSCAD for those who don't already have it installed.
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