Re-building a laser cutter

[Ali Kat]

Hi Guys,

I'm not new to the zone as I've built a couple of 3 axis routers previously but I've never played with lasers before.

I recently bought a fire damaged Epilog laser cutter with a 30w laser installed. The machine belonged to a friend and I had seen it working a few times and was quite impressed. Unfortunatly, it caught fire one day and caused quite a bit of damage to the enclosure and the drive motor wiring. The laser unit itself was untouched and the mirrors appear to be OK. I bought the machine off the insurance and it has since been lying in storage while I decided what to do.

I am considering taking the laser unit out of this machine and incorporating it into an existing 3 axis ballscrew machine that has a more useful cutting area than the Epilog.

Some feedback would be appreciated. Is it fairly straight forward to take out the laser and mount to another machine? Would an increase on the X axis from 600mm to 1500mm have any affect on the laser power? What peculiarities might I come across using a laser instead of a HF spindle?

I have to balance the above questions against the original intention which was to restore the machine to original working condition and sell it or part ex it against a good quality 3 axis HF router system.

Your thoughts would be appreciated.

Regards

Nick

[zax15uk]

Nick,

It really depends on what you want to use the machine for. The router will be able to do things the laser can't, and vice versa.

If you do decide to retrofit the laser onto an existing router system, keep in mind the safety concerns and that the mirrors / lens need to be kept very clean.

As far as actually implementing the laser onto the router, it should not be too difficult. If the unfocused spot size is still within say 75% of the mirrors and lens surface area at the maximum distance (Y+X+Z) then it will not result in any significant power loss. If you find this not to be the case then you would require additional optics or concave mirrors to recover the beam before focusing. At this point, the costs would become prohibitive.

So depending on your application, I would probably suggest to rebuilt the Epi although the final decision would be determined by how badly damaged it is.

A good solution for adding a laser to an existing router is to use a solid state diode laser (Nd:YAG or fiber would be an excellent option). Again, the application would determine if this is the right decision.

Zax.

[Ali Kat]

Hi Zax,

Thanks for the feedback. I think I'm with you most of the way although you've got me when you talk about solid state diodes etc! How do these differ from what I have on the Epilog?

My main reason for fitting the laser to a home brew machine was to increase the x axis and narrow down the y axis. I will mostly be looking at cutting 1200mm x 300mm x 6mm plywood.

Am I correct to assume that smoothness is a priority over power with a laser set-up? I am thinking that the motors only need to smoothly move the X and Y axis around with a manual height set for the Z axis as there is cutting force involved. My concern is the axis speeds - when I watched the original machine running it moved at tremendous speeds whilst cutting.

Any other advice or thoughts would be gratefully taken on board as I don't want to start pulling the Epilog to bits and find that it was a waste of time.

Cheers

Nick

[zax15uk]

Nick,

Lasers have less mass to move compared to a router, and don't require the torque. This allows higher speeds with greater acceleration/deceleration.

I wouldn't think you'll be cutting 6mm ply THAT fast with 30W, but if you intend to do any engraving or other materials you may be speed limited.

If you remove the Z-axis motor/slide assembly to reduce weight you may be able to tune the X/Y axis for improved speed.

Have you considered how you would adjust the material up/down to focus?

A diode laser is much more robust compared with a CO2 tube, and can easily be retrofitted to the Z-assembly. It would move up/down to focus just like the spindle. However, your application is better suited to CO2.

Zax.

[Ali Kat]

Thanks again for your comments.
I'm doing some serious web surfing at the moment and beginning to understand some of the issues regarding laser cutters. Previous CNC machine builds have been more for the sake of designing and building a machine than for a specific cutting purpose. With the laser idea, I have definite goals - I want to be able to cut light plastic, balsa and plywood up to 6mm for model building. I suppose I might do some engraving at some point in the future but this is not a pre-requisite.

I now believe that speed should be a major focus of any design and my thoughts are turning to belt drive on X and Y with a manual screw adjustment on the Z for focusing (I intend only to cut in 2D on flat material up to 6mm) this way I don't beleive that I will need a "raise and lower" type of work table. If I'm making sense so far, would I be correct to think that I would only need two mirrors if the laser was mounted parallel to the X axis - one to turn the beam onto the Y axis and one to turn the beam vertically down through the final focus lens? It is this lens that I would propose to arrange on a srew adjustment to accomodate different thicknesses of material.

The axis guides would probably be supported chrome plated or stainless round bar with open linear bearings on the X axis and twin round bar on the Y axis with closed linear bearings. I'm thinking the whole thing could be supported on a modified office type desk frame with the top removed. This could be a very cheap route for construction compared with ballscrews and THK type linear ways and carriages that I have used in the past. I am considering the use of the Epilog servo motors also as these appear to have been unscathed by the fire and need only new cabling.

As I think the design through, I see that a potential concern could be the acceleration and deceleration creating reactions on the table and causing vibration etc. My initial reaction is to limit speed of the axis and add weight to the table frame to dampen and reaction.

Everything is in my head at the moment as I am in the middle of a duty offshore but I will be returning home on leave shortly and will be keen to rummage around my parts collection for suitable components. Please keep the comments coming and any help in pointing to a build log of such a machine as the one I'm thinking about would be good.

If this thread turns into a build then I promise that I will take some pics and upload as I go along.

Cheers

Nick

[zax15uk]

Nick,

Building from scratch certainly opens up the options, and allows you to better match the table to a laser. Yes, belt drive is the way to go for a low torque, high speed application - and to keep the cost down.

You could do as you say and use just 2 mirrors although it is more common to have the tube mounted across the back (with a 3rd mirror), this keeps the overall machine more compact. A manual Z-axis for focus would be fine.

I don't see any major issues with your proposed design, just keep friction low.

Zax.

[LeonS]

Would you adjust the lens without moving the 45 degree mirror? If you moved the mirror and lens it would throw your beam out of alignment. Right?

Regards,
Leon

[zax15uk]

Correct. You would have a fixed 45 mirror and just move the lens up/down for focus.

Zax.

[the4thseal]

so how much is a fiber laser to do this. the price just always seems way out there.