aluminum is not really a good medium to continually use a threaded clamp in, the threads get stressed over time

That's probably why I've never seen a repetition fastener in aluminum. Mostly what I see in aluminum is stripped threads where the mechanic before me tightened the bolts like he was working in steel.
That last little, "good&tight" that works so well in steel will pull the threads out of aluminum every time.

That's why I own an inch-pound torque wrench.
Transmission valve bodies are way too expensive to guess at!

 

That's probably why I've never seen a repetition fastener in aluminum. Mostly what I see in aluminum is stripped threads where the mechanic before me tightened the bolts like he was working in steel.
That last little, "good&tight" that works so well in steel will pull the threads out of aluminum every time.

That's why I own an inch-pound torque wrench.
Transmission valve bodies are way too expensive to guess at!

It's going to be fairly light use. and if I strip something I just replace the stock, no big deal. Working in aluminum will be a whole lot easier that steel.

 

I am trying to create a clamp jig for my cheap CNC machine.

Is this a mill or a router table?
Mills usually come with a T-slot table which accommodates T-head clamps.
Max.

 

My siggestion is that you use additional rails, instead of tapped holes, to slide the clamps along the axis.

I need a downward force. Are you suggesting having myh clamp slide between two rails?

If so.

1. How would I exert downward force on the PCB to keep it in place?

2. How would I get the PCB under my "clamp" if the "clamp" is between the rails?

 

Is this a mill or a router table?
Mills usually come with a T-slot table which accommodates T-head clamps.
Max.

One of these:

Yes it has slots but the bed is aluminum. My plan is to replace with MDF. I did not want to risk drilling into aluminum. Plus considering the cheap cost of the machine, there is no guarantee the table is completely flat. I can mill mdf flat and replace ever so often if the suspect warping.

I did consider routing my own slots but then came up with this jig idea.

 

I need a downward force. Are you suggesting having myh clamp slide between two rails?

If so.

1. How would I exert downward force on the PCB to keep it in place?

2. How would I get the PCB under my "clamp" if the "clamp" is between the rails?

Can you post a photo of your machine, so we can look at the details?

EDIT: We cross-posted!

Why not place a piece of MDF on top of the aluminum bed, and then take advantage of the side slots?

 

There is also 3rd party t-slot table here http://www.cncroutersource.com/cnc-router-table-top.html
or..

If worried

About drilling in to the aluminum, you place a sacrificial surface on top.

Max.

 

Can you post a photo of your machine, so we can look at the details?

EDIT: We cross-posted!

Why not place a piece of MDF on top of the aluminum bed, and then take advantage of the side slots?

How would I get to the slots? Make the MDF smaller?

 

How would I get to the slots? Make the MDF smaller?

I mean the side slots. The slots that are vertically oriented.

 

I mean the side slots. The slots that are vertically oriented.

"Side slots"??? The ones on the edge?

 

I once saw a machine that used a vacuum pump to suck air from underneath a piece of MDF, its porosity would then help hold the work piece while it was being drilled and routed on. No clamps needed!

 

There is also 3rd party t-slot table here http://www.cncroutersource.com/cnc-router-table-top.html
or..

If worried

About drilling in to the aluminum, you place a sacrificial surface on top.

Max.

That is what I have.

 

"Side slots"??? The ones on the edge?

Exactly

 

I once saw a machine that used a vacuum pump to suck air from underneath a piece of MDF, its porosity would then help hold the work piece while it was being drilled and routed on. No clamps needed!

That could be a difficult mod with this machine.

 

Max.

 

That could be a difficult mod with this machine.

it could... but maybe not too difficult. You could remove the aluminum bed, and then replace it with a box completely made of MDF. All you'd have to do is seal the side and bottom sides with lacquer, and drill a hole that you could use to connect a vacuum hose to.

 

Exactly

Make some sort of clamp that hooks into that slot?

Then I imagine "straps" across the work piece?

Any ideas on how to do that? Take not of the clearance for the gantry.

What I like about replacing the existing table is it gives me a lot more Z clearance. With that MDF in place, replacing tools is a challange.

 

it could... but maybe not too difficult. You could remove the aluminum bed, and then replace it with a box completely made of MDF. All you'd have to do is seal the side and bottom sides with lacquer, and drill a hole that you could use to connect a vacuum hose to.

Interesting.

 

With that MDF in place, replacing tools is a challange.

So make the whole MDF box in a way that would be easily removable!
EDIT: The main advantage would be that you'd guarantee that the entire PCB would be laying flat across the surface!

 

it could... but maybe not too difficult. You could remove the aluminum bed, and then replace it with a box completely made of MDF. All you'd have to do is seal the side and bottom sides with lacquer, and drill a hole that you could use to connect a vacuum hose to.

My questions would be.

How much clearance between top an bottom.

Where would I get fittings for the pump?

How much vacuum would I need?