Tolerance and Smallest Bits Allow

[bonpon]

Hi all,

I am kind of new to CNC machining, so please bare with me.

Here is my situation:

I want to create a piece of MDF "insert" that would be inserted into a bigger piece of MDF as shown in the picture.

If I tell CAD and CAM software to cut the bigger MDF piece with an opening width of 30 inches, what dimension should I tell CAD and CAM program to cut the inner piece so that the gap is as small as possible but not touching each other?

I am going to use an entry level CNC machine like Shopbottools. According to them, the machine has a tolerance level of 0.005" with no loads applied.

The problem with above method is that I have to use 2 MDF slaps. 1st slap with the middle cut out and the 2nd slap with the outside cut out. So my another question is, rather than using 2 MDF slaps, what is the smallest bits size available I can use to cut 1 MDF slap into 2 pieces? Obviously, the gap will be a lot bigger than the first method, but I would save a lot of material.

Thank you!

Bonpon

[Pplug]

It all depends on how thick the MDF is and how fast you want it cut. I could cut up to 1" of MDF with a 1/8" bit. You could probably cut up to 1/4" with a 1mm bit in multiple passes, real slowly, 7ipm.

[LaserImage]

I would find someone with a laser to cut that for you. It would be way more efficient and you would have a kerf of about .005" - a little more due to the burn.

Gary

[bonpon]

That's interesting using laser! Do you know who make the laser that can be fit with most CNC machine?

[LaserImage]

Originally Posted by bonpon That's interesting using laser! Do you know who make the laser that can be fit with most CNC machine?

It is possible to retrofit a laser to a cnc machine but it's probably not cost effective unless you are cutting lots of parts. And, if you are cutting lots of parts then you would be better off buying a laser from a brand-name manufacturer.

I would find a local shop with a laser and see what they would charge.

[Geof]

I do not think it is practical to try and cut everything out of one piece.

It would be possible by going very slowly to cut the piece outer with a small cutter such as 1/8" and a 1/8" gap is very large between two pieces fitting together.

Make your hole tolerances above the size; i.e. 30.00" minus 0.00" plus 0.01".

Make your insert tolerances all below the size and also make it a little smaller for clearance; i.e. 29.98" minus 0.01" plus 0.00".

Also you need to call for radis on the corners of the insert. The corners of the hole are going to have a radius from the cutting tool; this is unavoidable. If you specify a 0.20" radius for the hole and a 0.19" radius for the insert it will fit neatly.