New jig to make P90 bobbin centers

[belwar]

Hey,

So excited about my new jig I thought I would share a few pictures. I made a jig over the weekend to make the acrylic centers for P-90 bobbins. I've been making them by hand and that just sucked. So I found a scrap piece of aluminum and threw it in the CNC machine and voila! 16 pieces at a time with an accuracy of 0.0025 which is more than accurate for me. I know its a stupid jig but anytime I make something faster and better I get so excited!

First I vacuum down a small piece of cast Plexi, then I thickness it with a large 1" router and drill the mounting screw holes through the plastic. Then I take that sheet of plastic and screw it down to the jig with 5-40 machine screws and route the perimiter with a 1/4" router bit. Then unscrew them and done. From start to finish it takes maybe 45-60 seconds a piece including load time.

I'm building a jig to make the top and bottom now. I'll post those pictures when im done.

belwar.

[Kesha]

Excellent work!

Very gracefully.

[belwar]

Part two

Well I've almost completed the second part of my jig to make the P-90 bobbin tops & bottoms, plus a basic mounting plate to hold the magnets in place. This jig should work like a hot damn when its finished tommorow. It will allow me to make bobbins out of pretty much any material. I'm probably going to use XXX paper phenolic (bakelite) because of its low di-electric properties. I looked at forbon and the stuff just looks curved and difficult to work with.

My plan right now is to route a small channel in the bottom and top of the bobbin and locate the bobbin center inside. Once glued together I re-load them into this jig and drill & tap (by CNC) the holes for the pole screws and mounting screws. I like the new Mojo screws but they are too tight for a standard 5-40 hole so I found a couple of oversized 5-40 taps and will probably use those.

I like the fact that with this I have complete control over the coil. I can control the height of the coil, and the size of the core. Let the experimentation begin!

belwar

[belwar]

Finished the second jig today!

Well I finished the second of the two jigs to make P-90 Bobbins today. It's a multi step CNC operation that cuts the bottoms & tops, then drills all the holes and taps them with 5-40 thread. I was working with phenolic and was having adhesion problems so I switched to acrylic, which also have relatively low di-electric properties. Here are some pictures of the finished jig with some of the finished product bobbins.

Right now i'm thicknessing down 1/8" cast plexiglass, but I've ordered the correct thickesses so the bobbins will be nice and shiny!

belwar

[StarryNight]

wow, I love seeing operations like this. very inspiring. As I'm nowhere near getting a cnc machine, i wonder if it would be possible to buy 3/4 (1"?)plexi and dado or route the inside to the specific depth essentially making the bobbin out of one piece. I wouldn't know the cost for stock like that but I imagine it would be expensive (and a lot of waste). I guess you can't route plexi on a high speed either without making butter! what's good rpm for cutting plexi?

[belwar]

i wonder if it would be possible to buy 3/4 (1"?)plexi and dado or route the inside to the specific depth essentially making the bobbin out of one piece. I wouldn't know the cost for stock like that but I imagine it would be expensive (and a lot of waste).

Believe it or not, im thinking of testing that exact premise tommorow or sunday. I have a 0.25" Thick, 3" diameter saw with 72 teeth which I use to cut truss rod slots. The blade is mounted horizontally instead of vertically. Being 0.25" thick i figure it would be perfect to test the one piece bobbin. Im going to put my vise in the machine, load an elevated block into it and drill/tap the low & high "E" pole screw holes. Then I'll put a piece of 1/2" plexi in there and drill/tap the low & high "E" pole screw holes. Screw it down and then then "key hole" machine the center of the bobbin. I tried just vacuum but the piece flies off and hits the door with a big BANG. Scary as hell I'll let you know how it works. I've been making test bobbins so far and they turn out pretty darn good if you ask me.

I guess you can't route plexi on a high speed either without making butter! what's good rpm for cutting plexi?

Heck no! Plexi machines like a DREAM! .. With one kicker. You MUST use cast plexi. Extruded melts and burns, and doesnt laser. Cast plexi is a little more expensive but machines like wood. You can route, laser, table saw, bandsaw, join, sand, you name it. I love cast plexi. My CNC's can go to 15000 RPM and machine in Inches per Minute... Here are feedrates I use

Routing with a 1/8": 14000 RPM, 25 IPM
Routing with a 1/4": 14000 RPM, 30-60 IPM
Routing with a 1": 10000 RPM, 50-65 IPM.
Drilling with a #38 upto 1/8": 3000 RPM, 15 IPM with Peck Drill
Tapping 5-40: 15 IPM with matching RPM.

Ask you local plastics store if they have "Cast Plexi Remnants" Then you dont have to buy a whole sheet.

[Joe Gwinn]

Plexi machines like a DREAM! .. With one kicker. You MUST use cast plexi. Extruded melts and burns, and doesnt laser. Cast plexi is a little more expensive but machines like wood. You can route, laser, table saw, bandsaw, join, sand, you name it. I love cast plexi. My CNC's can go to 15000 RPM and machine in Inches per Minute... Here are feedrates I use

Routing with a 1/8": 14000 RPM, 25 IPM
Routing with a 1/4": 14000 RPM, 30-60 IPM
Routing with a 1": 10000 RPM, 50-65 IPM.
Drilling with a #38 upto 1/8": 3000 RPM, 15 IPM with Peck Drill
Tapping 5-40: 15 IPM with matching RPM.

Ask you local plastics store if they have "Cast Plexi Remnants" Then you don't have to buy a whole sheet.

Are you cutting dry, or with coolant? If coolant, which one? Plain water? (Oil causes subsequent crazing of the surfaces.)

[belwar]

Are you cutting dry, or with coolant? If coolant, which one? Plain water? (Oil causes subsequent crazing of the surfaces.)

I machine it totally dry. I've been using a drop of rapid tap when taping the 5-40 screw holes but that has come to end now because of my new spiral tap. I see no need to lube cast plexi. there is virtually no heat. if you really were worried about heat you could probably cool it with compressed air alone

[Joe Gwinn]

I machine it totally dry. I've been using a drop of rapid tap when taping the 5-40 screw holes but that has come to end now because of my new spiral tap. I see no need to lube cast plexi. there is virtually no heat. if you really were worried about heat you could probably cool it with compressed air alone

OK. At those RPMs, most of the heat may be going into the chips. My mill won't go nearly that fast.

I'd be tempted to use some air and perhaps a vacuum hose to keep the cutting area clear.

[belwar]

OK. At those RPMs, most of the heat may be going into the chips. My mill won't go nearly that fast.

I'd be tempted to use some air and perhaps a vacuum hose to keep the cutting area clear.

For safety sake you can use a vacuume hose, However blowing air on it while you are manually working it causes a serious mess. The chips/dust are so light they blow all over the place. With cast there is very little heat.

What speed can your mill go? I can give you some feedrates based on those speeds.

[Joe Gwinn]

For safety sake you can use a vacuum hose, However blowing air on it while you are manually working it causes a serious mess. The chips/dust are so light they blow all over the place. With cast there is very little heat.

OK. I've never milled plexiglass.

I would not have guessed that there was such a difference between cast and extruded. They must be different materials, united by a common marketing story.

What speed can your mill go? I can give you some feedrates based on those speeds.

The max is 3400 rpm. It's a manual mill intended for metal, and weighs about 1500#.