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- Feb 8, 2014
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I got started on the router project that I mentioned in this thread http://www.hobby-machinist.com/threads/cnc-router-its-alive.38222/
The total run is 208 parts, 104 left and 104 right pieces. These are brackets for a luggage rack for a local outdoor recreational equipment manufacturer. Made from 1.25 thick UHMW, about 13 x 3 inches. Three 1.00 pockets, 0.90 deep, and an outside profile. The top surface is a series of blended arcs and the bottom is straight but will be cut with a 5.0 radius in a second operation. The top edges are also rounded over with a 0.25 radius in a second operation. There will also be two 0.25 mounting holes drilled through the width and counterbored in another operation.
The first operation is to cut the pieces out of a 48 x 96 sheet on the router. I'm using a solid carbide, 0.25, single flute, high helix bit designed for cutting soft plastic. Running 100 IPM feed and 13,000 RPM, 0.375 DOC per pass. Using the 0.25 bit I am able to nest the parts tight to get maximum yield from the sheet. The parts are spaced at about 0.270 all around, so not much wiggle room. I'm leaving 0.020 material thickness at the bottom to maintain the vacuum integrity over the entire sheet. It takes about 10 minutes to cut out one pair, so about 520 minutes of run time for one sheet.
Here is a picture of the first test cuts. Cutting a bit deep on these. I've since made adjustments.
Next operation is to round over the edges, 1/4 inch R corner rounding bit on on a Craftsman router table. I attached a scrap piece of UHMW to the table because I found that the aluminum table was scratching the parts. This operation takes about 30 seconds. And watch your fingers. This part already has the 5 inch radius cut on the bottom
For the next operation the 5 inch radius needs to be cut on the bottom surface. This is a project for the mill. A fixture needs to be built to hold the parts. Bolt the MDF base to the mill table.
Then add two more pieces to the top of that, glue and screw together.
Then profile the outside to provide a witness surface to be able to set it up for the next time it's used.
Then do the pocketing for the parts and the pockets over the bolt holes so you can get it off of the table.
Here is the 5 inch radius bit, it's about 2 inches diameter at the top.
This is done in three passes at full depth, once down the center then step over and take the last 1/4 inch or so off of each side. About 3000 RPM, 30 IPM. The clamps are set up to put pressure both down and back on the part to keep it tight to the fixture. A few seconds after this picture was taken, the tool grabbed the part, broke the clamp bolt, and threw the part on the floor. Hmmmm....time for plan B.
So the new clamping system, seems to work fine now. I need to make a HF run this morning to get four more 3 inch C-clamps. I was able to finish out the First Article parts for customer inspection. Once I get the go ahead I'll run the rest of them.
I haven't built the drill fixture yet because I'm still waiting on the tooling. That will be in the next installment.
.
.
The total run is 208 parts, 104 left and 104 right pieces. These are brackets for a luggage rack for a local outdoor recreational equipment manufacturer. Made from 1.25 thick UHMW, about 13 x 3 inches. Three 1.00 pockets, 0.90 deep, and an outside profile. The top surface is a series of blended arcs and the bottom is straight but will be cut with a 5.0 radius in a second operation. The top edges are also rounded over with a 0.25 radius in a second operation. There will also be two 0.25 mounting holes drilled through the width and counterbored in another operation.
The first operation is to cut the pieces out of a 48 x 96 sheet on the router. I'm using a solid carbide, 0.25, single flute, high helix bit designed for cutting soft plastic. Running 100 IPM feed and 13,000 RPM, 0.375 DOC per pass. Using the 0.25 bit I am able to nest the parts tight to get maximum yield from the sheet. The parts are spaced at about 0.270 all around, so not much wiggle room. I'm leaving 0.020 material thickness at the bottom to maintain the vacuum integrity over the entire sheet. It takes about 10 minutes to cut out one pair, so about 520 minutes of run time for one sheet.
Here is a picture of the first test cuts. Cutting a bit deep on these. I've since made adjustments.
Next operation is to round over the edges, 1/4 inch R corner rounding bit on on a Craftsman router table. I attached a scrap piece of UHMW to the table because I found that the aluminum table was scratching the parts. This operation takes about 30 seconds. And watch your fingers. This part already has the 5 inch radius cut on the bottom
For the next operation the 5 inch radius needs to be cut on the bottom surface. This is a project for the mill. A fixture needs to be built to hold the parts. Bolt the MDF base to the mill table.
Then add two more pieces to the top of that, glue and screw together.
Then profile the outside to provide a witness surface to be able to set it up for the next time it's used.
Then do the pocketing for the parts and the pockets over the bolt holes so you can get it off of the table.
Here is the 5 inch radius bit, it's about 2 inches diameter at the top.
This is done in three passes at full depth, once down the center then step over and take the last 1/4 inch or so off of each side. About 3000 RPM, 30 IPM. The clamps are set up to put pressure both down and back on the part to keep it tight to the fixture. A few seconds after this picture was taken, the tool grabbed the part, broke the clamp bolt, and threw the part on the floor. Hmmmm....time for plan B.
So the new clamping system, seems to work fine now. I need to make a HF run this morning to get four more 3 inch C-clamps. I was able to finish out the First Article parts for customer inspection. Once I get the go ahead I'll run the rest of them.
I haven't built the drill fixture yet because I'm still waiting on the tooling. That will be in the next installment.
.
.