I needed to cut holes for speakers but also to carve notch for speaker edge to fit in. As I did not have proper tool for that job I had to make it on my own. As I already had cutting guide adapter for my Proxxon grinder I decided to make an adapter for it using 3D printer. It was actually adapter for Dremel tool with customization to fit Proxxon, so new tool may be used with both Proxxon and Dremel grinders.
I did modeling in FreeCAD and printed it on my Prusa MK3S 3D printer. It did a job surprisingly well.
Tool consists of these 3D printed parts:
– sliding bolts (3 pieces),
– nut caps (3 pieces) and
– needle holders (as much as you need).
Other than that you would need:
– Cutting guide adapter (eBay example)
– M6 nuts (3 pieces),
– M6 Serrated lock washers (3 pieces) and
– something to be used as needles (nails, strong thin wire, tube or something similar) size that fits your needs.
Tool body has one circular and one linear slot. Cutting guide adapter (with grinder) should be inserted in circular slot. It will snap nicely but loosely enough that it could be rotated.
The other slot is for rotation center needle sliders. Slider is inserted in slot from bottom, and fastened using M6 nut and M6 serrated lock washer. Serrated lock washer is a must to prevent nut loosening up due to vibrations. You can also mount nut cap for better grab.
You do not need tools to tighten sliders, finger strength is enough.
Sliders have hole on the bottom. That is used for inserting needle holder. You can have several needles various diameter and length. This allows easy change of a needle.
You have to make needle by yourself. Use nail, strong tin wire, tin tube or something similar that suits by diameter and length. Needle 2 to 3 mm in diameter should be enough for the most purposes. Needle should tightly match drill used for center hole to avoid any wobbling. Needle should go all the way through needle holder but not to protrude on the other side.
You have to insert needle into holder as tightly as possible. Use glue. It should not be loose to fall of. If none of the holder models provided fits make your own by altering holder hole size in one of existing models.
If it happens that, when you try to pull out needle holder from slider, needle comes out but holder body is left in slider that means needle was not tight enough. You can use small notches on top side of slider to push out holder body which is stuck. You have to remove slider from tool slot to get access to those notches.
How is tool used
If you have to just to cut fixed radius it is simple to use this tool. All you have to do is to have needle fixed at appropriate position matching needed radius. Tool is then rotated until cut is done.
You can set radius by measuring distance between center of the needle and outer or inner edge of the cutting tool, depending on your needs.
Easier way is to mark center of the radius you have to cut, and also draw cutting line. Make hole in center of the radius. Hole size should match needle thickness to avoid any wobbling. Position tool so that needle is in the center hole. Needle should not be too long to protrude on the other side of the material you are cutting.
Set grinder cutting bit so it is leveled to the surface of material. Loosen needle slider so you can easily move tool to change cut radius. Move it until outer or inner edge (depending how you want to cut) of the cutting bit matches cutting line. Fasten needle slider.
Now you can set bit to cutting height, and rotate tool until you finish cutting.press whole tool firmly on the surface of the material you are cutting, but not too much so it cannot move.
Do not cut too deep at once. That could be to hard for grinder, cutting tool and material itself. It is better to go in shallow steps and repeat cutting in several passes until needed depth is reached.
You can also do notches wider than cutting tool by using limiters. Limiters are actually needle sliders but without needles. So, you should have three needle sliders inserted in slot, with needle inserted in the middle slider. Other two sliders would serve as limiters.
You can set tool by measuring distances, but, again, it is much simpler to draw cutting lines at material you are going to cut and them place tool and align using those lines.
Insert needle in center hole and loosen slider to easily move. For outer cutting line, set needle in position that outer edge of cutting bit is aligned to that line. Secure needle slider so it cannot move and then move outer limiter to be tightly seated next to the needle holder and tight it. Now you can release needle slider and set its position to match inner cutting line with inner edge of cutting bit. Again, tighten needle slider and now move inner limiter tightly beside it and tight it.
Release needle slider but not too much, just enough that it easily slides. If you loosen it to much it would wobble.
Now you can do cutting. Freely move grinder in whatever direction you like. It would not go out of the area you have set with limiters.
Do not forget, you can rotate cutting guide adapter (and grinder in it) while cutting. That would allow setting it in position where you can better see what you are doing, and also „unwind“ power cord if it winds up due to circular motion.
Downloading and printing
You may download part models from:
Thingverse – https://www.thingiverse.com/thing:4656929
Print using PETG with at least four vertical, top and bottom horizontal shells and at least 60% infill. The more infill the merrier.
Positon parts exactly as in STL. Supports are not needed and not wanted as you need as smooth sliding surfaces as you can get.