CNC Routing or CNC Laser cutting for this job?

**stevec1234** · 10th April 2010, 11:15 AM

Hi everyone,

I am hoping you are all willing to give me your thoughts on what I am trying to achieve. I have drawn up a design for a mold to be used with gluing up veneer into ply wood cylinders.

There are two main components to the design. One being the "rib” (use picture 6 as reference). These will be machined from 2x 25mm ply, 5x 12mm holes which will be used to bolt the components together to have a solid half. The horizontal grooves (which bolted together it will equal a 16mm hole) will be used to bolt the two halves of the mold together using m16 threaded bar.

The 2nd component will again be machined with 25mm ply and have the 5x 12mm holes to line up and bolt the halves together. This second component will be stacked in groups of three to create a deeper mold. I have also added a male V profile and female V profile, refer to pictures 1&2 (or a rounded profile. refer to picture 7) on each half to help line the two halves up perfectly when gluing up the veneer. Which profile will be more affective when lining up the two halves and which will be more accurate when CNC machining.

It is crucial that the two halves line up perfectly and the ID of the mold is as close to perfectly round as possible and to a tolerance of +0 -0.1 in diameter.

In your opinion which cutting process is going to have the most consistency and accuracy so when assembled all these components line up properly? I was thinking of going with local company using a CNC router though someone mentioned to me they are not always accurate especially with repeat cuts and that laser cutting would be a better option.

How well do you the think the Router or laser would go cutting a perfect circle or would you suggest having the ID cut a couple of mm smaller originally and when assembled and the halves are bolted together to have the ID cut to its final diameter on a boring machine?

Any suggestions around the design and effective ways to line the two halves up when the glue up happens are welcome. I will also mention when the veneer is inserted into the mold the two halves will be open about 50mm and then when all the veneer is in position the two halves will be closed pulling the veneer into place.

Also there will be packing spacers in the four corners.

Please refer to the attached pictures to hopefully make things a little clearer.

Thanks in advance

Steve

**rodm** · 10th April 2010, 01:12 PM

I would not make the fixture from plywood as there is a risk when glueing up that it will stick to the fixture. Also plywood will change dimension with moisture content.
Have you thought about perspex, nylon, HDPE, etc. Aluminum might also be an alternative but is expensive and may have a reation with the glue leaving a stain on the veneer.

The rest of your questions are best answered by the person who is going to do the machining. They know their machine tolerances and can advise you on slight design changes to compensate.

Laser cutting will get to the inside corner of the "V" where a router or mill bit leaves a radius of the cutter on inside corners. This can be corrected in your design. I had some 10mm steel laser cut and the edges did not come out square. I don't know if this is becasue it was steel or that burning a light through material broadens or narrows the beam, or deflects the light by the time it gets to the other side. Again ask the operator as they will know.

As for your designs they all look fine to me and I would not pretend to know more than you on this. Looks like an interesting project and you have put a lot of thought into it already.

**stevec1234** · 10th April 2010, 05:59 PM

Thanks for the reply. My current forms are fabricated and machined out of steel. I am thinking this design when I expand on sizes. I use between 60-70psi of clamping pressure during the forming process to ensure a tight even bond. How do you think perspex or nylon will hold up under that much pressure?

How affective do you think the round profile would be for lining up the two halves?

I am thinking it will be best to cut a rough diameter and then a final machining to make sure the ID is perfect.

Thanks again

Originally Posted by rodm

I would not make the fixture from plywood as there is a risk when glueing up that it will stick to the fixture. Also plywood will change dimension with moisture content.
Have you thought about perspex, nylon, HDPE, etc. Aluminum might also be an alternative but is expensive and may have a reation with the glue leaving a stain on the veneer.

The rest of your questions are best answered by the person who is going to do the machining. They know their machine tolerances and can advise you on slight design changes to compensate.

Laser cutting will get to the inside corner of the "V" where a router or mill bit leaves a radius of the cutter on inside corners. This can be corrected in your design. I had some 10mm steel laser cut and the edges did not come out square. I don't know if this is becasue it was steel or that burning a light through material broadens or narrows the beam, or deflects the light by the time it gets to the other side. Again ask the operator as they will know.

As for your designs they all look fine to me and I would not pretend to know more than you on this. Looks like an interesting project and you have put a lot of thought into it already.

**rodm** · 10th April 2010, 06:52 PM

I'm not an expert but I would imagine 70 psi in 25mm material to be fine.

Boring the centre hole after cutting the parts will guarantee an exact fit. Perhaps you could also get a couple of steel dowels put in those parts before they bore the centre.

**stevec1234** · 11th April 2010, 01:24 AM

Originally Posted by rodm

. Perhaps you could also get a couple of steel dowels put in those parts before they bore the centre.

Steel dowels through the depth of each half? The plan is to have 5 bolts through the depth holding each half together as a solid unit. Can you please explain what you mean I didn't quite get it. Sorry

**rodm** · 11th April 2010, 02:30 AM

Should have been clearer. Instead of the notches to locate the halves but in steel dowels. On second thought it is probably no better than your locating notches.

**stevec1234** · 11th April 2010, 09:14 PM

Originally Posted by rodm

Should have been clearer. Instead of the notches to locate the halves but in steel dowels. On second thought it is probably no better than your locating notches.

Cheers. I have a similar concept on the steel forms.

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