Test build of the frame with CNC milled parts

No real progress on CNC for I destroyed my last 4 mm CNC bit.
But today I cut some of the studding and made a test build of the frame with my CNC milled corners.
Here is a photo of the frame on this winters last snow.



Next I am planning to make z-bar-top-clamps, y-motor-bracket, y-idler-bracket an y-bar-clamps.

First set of corner blocks milled

Bolting the milled piece to table worked like a charm.



After some fine tuning of the program results were really good.



And now I have first set ready.



The milling program needs still some fine tuning. The measures that I had for holes in the table were not quite on the spot so the centre holes are a bit misaligned in pieces that had the holes for bolting but this is not really a problem for these holes are not used.

Fasten Your block

I am going to bolt the milled piece on the vacuum table with m8 bolts. The vacuum table has holes for vacuum that are in 120 mm matrix and they are closed when not needed with m8 plastic screws.
Luckily the waste plastic pieces have two 8 mm holes that are 120 mm center to center.
Now I ONLY have to sift my program so that the milling head does no hit the bolts and even uses the existing holes. And bolting the piece makes it possible to mill at least partially through the plastic because I don't have to care about the vacuum.

Some progress

Today I tried again mill the corner blocks.
I lowered the spindle speed to 1000 rpm and it seems to bee about rigth for now I have no more melting plastic.


And even multiple ;-)


Milling time is under 4 minutes for one piece and 22 minutes for batch of six.

I still have some problems on keeping the slippery plastic on the CNC mills vacuum table.
I had to use a piece of MDF board that is sanded both sides so that only the core that is not so dense and passees vacuum through is left (16 mm board sanded to 10 mm) this has been a good way before with thin or other ways problematic materials but was not good enough so I added two sided tape between sanded MDF and plastic and it seems to help but is not feasible for mass production ;-) I probably have to make a jig so I can fasten the milled piece with screws.


Because I am using a vacuum table to hold the milled piece on it's place I have to mill the pieces so that about 1 mm is left to hold the vacuum. After milling I took the pieces apart with band saw and cleaned them with hand router that is installed upside down on a table.


Finally I deburred the sides with a knife.
I still have to drill the holes open to test the pieces.



After initial measurements it seems that the milled plastic is still moving a bit and is a bit warped on the milling table and so the milling depth varies +- 0.3 mm because of the double sided tape I used is not even thickness .

For next batch I will try fastening the plastic with screws on a MDF board and if that works I have to optimize the program for now it lifts the spindle over 100 mm when moving to make it run faster.

First steps

This is trying to be my blog of repstrapping mendel reprap 3D-printer.
I am going to try to mill parts from plastic with a cnc wood router.


Today I tried to mill corner blocks.


Results were not that good.
The router has a vacuum table that does not keep smooth plastic on the spot when milled.
From three trials I got only one that looks a bit like corner block half for mendel.

Next time I have to either attach the pastic to MDF board or make the bottom of the plastic rougher that it does not move when milled.

Other problem is that the milling bits are for wood and not quite right for milling pastic the chips tend to stay in the milled groove and some times melt in it so I have to find right feed and spindle speed by trial and error method.

Here is a link to DXF file I made of some mendel parts. There are several layers and on each layer is a part or variation of part.

meldel_parts.dxf

I am using this as base for CNC programs by importing this in CAM.