[OnezerO]

I am finalizing the design of my CNC table and I needed some input on what the optimal distance should be between my router collet and my spoilboard when my Z-Axis is at its maximum lowered position.
My Z-Axis has 11" of travel. I want to get the best distance to use the largest amount of different length router bits without having to raise my workpiece above the spoilboard.

What is the most common distance on other CNC machines?

What is the optimal distance?

Thank you all in advanced for your suggestions.

[jones]

I've designed mine so I can get the collet pretty much down to the spoil board so I can use short, rigid cutters on thin material.

Probably not necessary, I'll be interested to hear how other people have approached this design point.

Good topic!

[dharmic]

Not my design but I've found it useful. The gantry on my machine has about a 140mm clearance and the Z travel is about the same (smallish machine). The spindle is clamped to the Z table with a couple of rings which can be loosened off. So I can work nose-to-table as jones describes, or for taller work I can push the spindle up through the clamps and work on top of material that will clear the gantry, with room for tooling.

A longer Z axis would save having to move it around but, of course, that means more torque around the X axis and consequently a greater deflection under load or a need for heavier gantry etc.

[OnezerO]

Thanks for the quick reply. I have mine currently designed to sit 3/4" above the spoilboard. Hopefully we will see a lot of suggestions.

I've designed mine so I can get the collet pretty much down to the spoil board so I can use short, rigid cutters on thin material.

Probably not necessary, I'll be interested to hear how other people have approached this design point.

Good topic!

[OnezerO]

Interesting. Thank you. My router will be fixed in place so adjusting it beyond the 11" of travel is a redesign.

Not my design but I've found it useful. The gantry on my machine has about a 140mm clearance and the Z travel is about the same (smallish machine). The spindle is clamped to the Z table with a couple of rings which can be loosened off. So I can work nose-to-table as jones describes, or for taller work I can push the spindle up through the clamps and work on top of material that will clear the gantry, with room for tooling.

A longer Z axis would save having to move it around but, of course, that means more torque around the X axis and consequently a greater deflection under load or a need for heavier gantry etc.

[dharmic]

Believe me, you're likely better off that way too - the way this thing is built, tram adjustment around X or Y is nigh impossible (maybe via shimming) and changes every time I move it. Not such a big deal on a machine that's usually only running max 6mm dia cutters but, still, not ideal.

[ger21]

You want the smallest bit you'll be using to reach the spoilboard, and at the other end, you want the longest bit you'll be using toi be able to clear the tallest workpiece you'll be using.

[DonKes]

Temporarily add another thick spoilboard if you need to get closer. Only you know what your mix of usages are.

Don

[CitizenOfDreams]

You want the smallest bit you'll be using to reach the spoilboard

Gerry, we seem to be on the same brainwave frequency. I was going to make the same reply in almost the same exact words when I read your post. :wave:

[OnezerO]

Thank you.

[OnezerO]

Yes, you guys get me! So since I at the final design stage before starting construction of my table I wanted to know what distance you would use?

- - - Updated - - -

You want the smallest bit you'll be using to reach the spoilboard, and at the other end, you want the longest bit you'll be using toi be able to clear the tallest workpiece you'll be using.

Exactly, this is what I am trying to accomplish. Since I am new at the final stage of my design and I don't have a functioning CNC yet can you share what the two extremes are in the size of the router bits you use or the router bits that most applications require.

Thank you.

[OnezerO]

Temporarily add another thick spoilboard if you need to get closer. Only you know what your mix of usages are.

Don

Yes, this is a viable solution but only for smaller projects. Thank you for the reply.

[skrubol]

I'd go 1/2", as that's a common flute length for 1/8" cutters, but if you're already at 3/4" and you don't plan to use cutters that small very often, I'd just leave it and do as suggested and add another layer of spoil board when you need to cut small. What's your gantry clearance?

[ger21]

Exactly, this is what I am trying to accomplish. Since I am new at the final stage of my design and I don't have a functioning CNC yet can you share what the two extremes are in the size of the router bits you use or the router bits that most applications require.

Thank you.

It's nearly impossible to tell someone else what they need.
But from my experience,most people that don't know what they need, don't need nearly as much as they think they'll need.

On the machine I'm building, I have about 8" of travel, and 5" of gantry clearance. This allows the collet to reach the spoilboard, and lift a 3" bit high enough to clear the bottom of the gantry.

I would say that 99% of people will never cut anything thicker than 2"-3". And unless you are cutting foam, you most likely will never use bits longer than 3".

[wizard]

Yes, you guys get me! So since I at the final design stage before starting construction of my table I wanted to know what distance you would use?

Somebody already covered the basic idea, low enough to reach the spoil board with your smallest (shortest bit) high enough to clear you longest bit. I would extend this a bit though as you need to be able to surface that spoil board, this is usually not a problem as bits for surfacing are usually larger. Also you need to get close enough to allow for any fixturing that you might mill into the spoil board with the tooling you would use to do that. Generally getting to with 20mm should do it but consider what was just said.

Exactly, this is what I am trying to accomplish. Since I am new at the final stage of my design and I don't have a functioning CNC yet can you share what the two extremes are in the size of the router bits you use or the router bits that most applications require.

Thank you.

This is impossible to answer without knowing what exactly you intend to do with the machine. For example a guy concentrating on engraving will have a different series of tools as opposed to one machining components for his sail boat build. Likewise a guy doing PCB routing has a different set of tools compared to a guy making Guitar parts.