Help with aluminium bed for pcb's

[djh82uk]

Hi Guys

Since getting my kress making pcb's on my machine is down to a tee, however my current problem is that the boards are never flat, I cannot afford a floating head, nor do I have a lathe yet to make one.

Now I was using MDF and the surfacing wizard in mach 3, and I am pretty damn certain that the problem is the mdf.

So I have a load of 6" wide Aluminium (1/4" depth). So my question is how best to make the bed hold the pcb's?

I need 4 posts as offsets for when doing double sided boards, these also help make sure the board is alligned, my problem is I was using M3 threaded rod for the posts, but have snapped my 2 Taps for threading the holes (I was drilling 2.5mm holes, prob a tiny but more as my pillar drill is not very good)

However I have had success making M4 holes for some reason.

Initially i was going to make little aluminium plates bolted down onto the outer rim of the board, but after playing with it, it seems 3 M4 cap screws on each side of the board may suffice, what are your thoughts?

My other idea was to get some ali sheet, cut out the middle a little smaller than the board, and drill some holes, and lay that over some threaded rod that sticks up from the bed, then use nuts and washers to hold it down.

Im thinking that just using cap screws may be the easiest.

My other problem is that I only have 3.175mm and 8mm collets for my kress, so my machine cann drill the holes, and using the pillar drill is not accurate enough for my tastes.

What about milling the holes with say a 2.4mm bit?

What are your thoughts?

Any advice on tapping? I take it there is no easy way to tap holes using a Taig Mill?

Ive messed up two beds so far, am trying not to mess up anymore

DJH

[pminmo]

1st, 1/4" aluminum will move pretty easy under the pressure of screws. So, if your planning on that being a stable flat surface, I think you will be surprised. Once you figure out how to get your flat Al surface, a simple method I use is a few strategically placed dots of thin super glue. To remove the pcb from the Al plate that has been super glued, use acetone. The acetone melts the superglue.

[epineh]

I have used vacuum clamping with PCB's and the results are great, you may have to fashion something to suit your machine, but PCB's clamp so nice with a vacuum.

Russell.

[kreutz]

I am testing a machine for the same purpose, we made a vacuum clamp for the PCBs out of MDF after surfacing it parallel to the router head. Even with that clamp some of the copper clads still don't get flattened enough.

We are using a floating head (drilling and milling depth is adjustable with a micrometer) of our own design (and did not need a lathe to make any of its parts, actually they were made on a CNC'd Sieg X1).

Regarding the registration system employed to make double sided PCBs, we use two pins equally spaced from the board outline at 1/2 the length of the board on the x axis (we mirror the bottom side on the x axis). The hole on the PCB is made using a 3 mm drill, the pins are 1/8" diameter, tight fit on the hole. No problem at all with two sided alignment.

My 2 cents: A floating head is a must.

[djh82uk]

Thanks guys

With the 1/4" aluminium, Im not having the bolts go right through, just tapping the holes in the hope of not distorting it.

What thickness would you reccomend?

With regards the floating head, im very eager to work on one, I don't understand how you could do with the mill, do you have a rotary table?

Or am I thinking inside the box too much? I pictured using round aluminium stock with a bore and threaded end for a nut on the end to hold the endmill and collet in place.

Any ideas would be greatly appreciated.

Regards

DJH

[kreutz]

Originally Posted by djh82uk Thanks guys With the 1/4" aluminium, Im not having the bolts go right through, just tapping the holes in the hope of not distorting it. What thickness would you reccomend? With regards the floating head, im very eager to work on one, I don't understand how you could do with the mill, do you have a rotary table? Or am I thinking inside the box too much? I pictured using round aluminium stock with a bore and threaded end for a nut on the end to hold the endmill and collet in place. Any ideas would be greatly appreciated. Regards DJH

We used a short (about 6") linear rail with two trucks, on the upper truck runs the router, on the bottom one runs the foot that contacts the PCB surface. On the foot side (screw attached perpendicular to the plate mounted on the truck) there is a hole, concentric with the spindle axis (the milling bit or drill goes into that hole). On the front side we mounted a micrometer to separate both plates (the one that supports the router, screw attached perpendicular to the one mounted on the upper truck, and the lower plate that supports the foot). We also added a spring tensioner attached between the router assembly and the base plate (the one that supports the linear rail) mounted on the Z axis. The spring tension is adjustable in order to compensate for the router's weight, and serves to adjust the down force.

A photo will be more explanatory, but the machine is at a friend's home.

On the foot we also mounted a PVC tube that serves as a vacuum cleaner head concentric with the router's spindle, the tube's down edge is the one running on top of the PCB and makes the whole head follow the PCB clad's horizontal surface.

[unterhaus]

Originally Posted by kreutz We used a short (about 6") linear rail with two trucks, on the upper truck runs the router, on the bottom one runs the foot that contacts the PCB surface. On the foot side (screw attached perpendicular to the plate mounted on the truck) there is a hole, concentric with the spindle axis (the milling bit or drill goes into that hole). On the front side we mounted a micrometer to separate both plates (the one that supports the router, screw attached perpendicular to the one mounted on the upper truck, and the lower plate that supports the foot). We also added a spring tensioner attached between the router assembly and the base plate (the one that supports the linear rail) mounted on the Z axis. The spring tension is adjustable in order to compensate for the router's weight, and serves to adjust the down force.

Do you drive one of these two plates with a stepper motor?

[kreutz]

Originally Posted by unterhaus Do you drive one of these two plates with a stepper motor?

No, they are both floating. The base plate (where the linear rail is attached), is attached to the Z axis, and, of course, the z axis is driven by a motor.

[neilw20]

Originally Posted by kreutz I am testing a machine for the same purpose, we made a vacuum clamp for the PCBs out of MDF after surfacing it parallel to the router head. Even with that clamp some of the copper clads still don't get flattened enough. We are using a floating head (drilling and milling depth is adjustable with a micrometer) of our own design (and did not need a lathe to make any of its parts, actually they were made on a CNC'd Sieg X1). Regarding the registration system employed to make double sided PCBs, we use two pins equally spaced from the board outline at 1/2 the length of the board on the x axis (we mirror the bottom side on the x axis). The hole on the PCB is made using a 3 mm drill, the pins are 1/8" diameter, tight fit on the hole. No problem at all with two sided alignment. My 2 cents: A floating head is a must.

And heres my multi$'s worth. Instant floating head.
http://www.2linc.com/engraving_accessories_CT.htm