[Adaware]

I’m making some rough drawings of a small 3-axis VMC, but am a little lost when trying to figure out the Z-axis spindle clearance to table (no vise on table, only table) and Z-axis travel. It’s designed around a BT30 spindle.

I would like to have about 200mm Z-axis work height to be able to have enough clearance in case of 4/5-axis conversion. The X- and Y-axis travel will be between 250-300mm to get the machine to be somewhat proportioned due to the 200mm Z-axis travel.

Right now I have about 70mm of clearance from spindle nose to table when the Z-axis is completely lowered. Is that an okay number or is it to low/high?
Is there some “rule of thumb”?

Let's not consider the stability and rigidity of the machine at this point as this is later in the design process.

[chuckorlando]

Take the shortest tool you will need, that tool needs to reach the table. Seems you have just under 3in. If so, that sounds a little close. But then some tools are so small you might need it lower...

[Adaware]

I have done some thinking. This is a small machine so the piece to be machined would many times be clamped directly on the table since it will allow for more room in the Z-Axis.

To fasten any small tools in the BT30 spindle I will probably need an ER holder of some sort. The shortest ER16 holder I can find during a quick search is approx. 60mm from spindle to where the tool projection starts. I guess 10mm tool projection is the smallest I ever will use anyway so I think 70mm from spindle to table is a good start for now

[chuckorlando]

Sounds like it worked out just right. Good deal

[lcvette]

I have done some thinking. This is a small machine so the piece to be machined would many times be clamped directly on the table since it will allow for more room in the Z-Axis.

To fasten any small tools in the BT30 spindle I will probably need an ER holder of some sort. The shortest ER16 holder I can find during a quick search is approx. 60mm from spindle to where the tool projection starts. I guess 10mm tool projection is the smallest I ever will use anyway so I think 70mm from spindle to table is a good start for now

Don't forget you will need to be able to change longer tools such as drills and such that tend to be longer as well. That is a really small machine for a bt30 spindle. 4th and 5th would be impossible most likely as they usually require longer tools for the head and spindle to clear the rotary or trunnion tables and the parts are higher up usually too. I would give yourself 50% more z travel then you think you'll need and I'm sure even then you will find you need more for some work holding requirements.

Chris

Sent from my QTAIR7 using Tapatalk

[chuckorlando]

No arguing with that. Real Estate has location and machining has capacity, capacity, capacity.

[Adaware]

BT20 was my preferred tooling for this size of machine, but was quickly discarded because it was so hard to find tool holders and spindles in that size.

You're right about the 4th and 5th.

The machine can probably not be too big, but the wallet can quickly become too small!