Step 24: 4th Axis (MDF Structure)

posted in: Construction CNC DIY | 1

4th axis

I finally started to machine the parts of the structure of my fourth axis. The design is already validated, I modified some other things, but basically this complete and ready for manufacturing. But before I start cutting wood, I’ve wanted to do a number of tests, as there are some operations that require some precision. For example external measures of the plates, the position of the holes and overall, the diameter of the bearing housing. I’ve had to do many tests, adjustments and go modifying the machining program, until finally I could find which was looking tolerances.

I specifically, I prepared a small and easy to machine piece, which had all the holes and typical examples of this structure measures to check tolerances: Hole with accommodation for screw head hole Ø12 nuts for drum housing for bearing, and of course external action. I’ve been changing different settings, until I finally found the functional tolerances, so I have: for Ø28mm bearing, accommodation Ø27.92mm. Screw drum Ø12mm, Ø11.9mm hole for external action as a 30×60 rectangle, it would stay at 30.1 x60.15mm which for me is more than enough. So once set all plays start cutting MDF!

Obviously you must first program the G code, for which I use CATIA, as I have said in previous posts. After much testing, I have found the ideal mill for cutting MDF, and the optimal conditions: 20,000 rpm and feed between 500 and 700 mm / min, with a depth of 2 to 3mm past. As there are many pieces that have many holes, and basically all the parts share the same type of operation, I have tried them all with the same pattern of operations. Basically it is a first step to make all the holes at once, and a second to outline the perimeter and cut the part.

So get to work:

How many parts are similar, and the operations are basically the same, I will not hang as many more images of mechanized, only brief examples, to see the cutting conditions.

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This is one of the most simple parts but still I could see that the cutting conditions studied have previously paid off. I have a dimensional tolerance of +0.1 +0.2 perimeter cut, more than enough for what I need. The position of the holes is accurate. And in other parts where I have to embed the bearings, they get hammered, but just entering without breaking the wood and with a very good press. Even the screws go tight barrel, which is also very positive.

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So a few hours later, I had almost all machined parts:

Cuarto eje: todas las piezas

Now it’s time to assemble

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These are the famous barrel screws, hammer entering, very tight. Perfect.

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The bearing in place, also entering hammer, and I could not resist to try the shaft

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The motor mount plate also fits perfectly.
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Leaving the motor in place according to design

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How the pieces fit each other? it really well. You have to adjust a little barrel screws to fit, this is not an exact science, but after all the steps are perfect for what I need.

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This is the structure of counterpoint. It has become very rigid

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And here the two structures, the motor and counterpoint.

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For the bottom, I put these inserts for wood, screwed to the counterpoint in different positions. Even some small adjustments but I lack, but in principle, the important thing is already done.

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And now the final set. Looks good as it is becoming everything. In summary, you could say that the router allows me to produce parts with sufficient accuracy, provided that the right tools are used. I struggled, but finally finding the right cutters, this is critical. I can machined fits and tolerances that I need, right before I do my tests. Perhaps the negative side is the time it takes, as long I did not want to force the machine, the feed rate was 700 and the depth of 2-3mm past, which have been almost all day to machine these parts. This means burning aspiration, strawberry, mandrel, etc. .. making noise, dust .. we all somewhat uncomfortable (sorry for my neighbors). Maybe could try to increase the cutting conditions, but do not want to burn the electronics, so I’d rather not risk it.

Despite this, I am happy with the experience because I have proven that my machine is capable of machining parts and make useful sets of machines with the precision required.

I’ll make a new post when finished assembly.