Half-inch bit limitations


I understand that an 80 mm spindle and ER20 collet will let you run 1/2" bits, but I’ve seen comments to the effect that not everyone is comfortable doing this on their Onefinity machines. What are the limitations?

For context, I want to carve deep (up to 1.65") pockets, a few to several inches on a side, in 8/4 hardwood stock. I have been doing this on an ancient and venerable makerspace machine using a long 1/2" bit, after having some mild but noticable deflection issues with long 1/4" bits. I want to reduce deflection, not increase feed rate.

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Howdy Tobias!

I have been using an 80mm spindle and 1/2" bits for a since I’ve had the machine for more than a year and I have no issues… EXCEPT… the larger the diameter of the bit the more force is applied to the work piece. Make sure your hold down system is perfect or the work piece will move. I use carpet tape and hold down brackets, PLUS blocks butted up to the sides as well. Works good!


Hey Tobias,

this was discussed here occasionally. Deflection could come from the fact that on the Onefinity, the Z carriage moves with only one linear bearing per rail:

Image: Onefinity 80 mm spindle mount (for Standard Z-16 Slider). The spindle mount seen here is 2″ (51 mm) high and the linear bearings seen here are 70 mm long, the Z axis travel is 133 mm.

Most CNC mills have two linear bearings per rail, as can be seen here, here (RoverCNC), or here (Sorotec Alu-Line).

Users thought of mounting two 80 mm mounts on top of the other or to simply mount an Universal Z assembly. This would also allow to use the spindle clamps that are usually sold by spindle manufacturers, allowing for other spindle diameters.

Onefinity now offers a Z-20 Heavy Duty Z Slider with 20 mm diameter chrome-plated hollow shafts and 165 mm Z travel that you can retrofit to the Standard Series machines and which replaces the original Z-16 Z Slider with 16 mm shafts, but the spindle mount still runs with only one, however bigger, linear bearing per rail.

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So is there a router option for 80mm

I have looked all over the forum but only spindles are discussed

Just wondering


Hey Dan,

hand trim routers have a diameter to hold them in your hand, e.g. the Makita 65 mm, the Dewalt 69 mm.

The 80 mm mount was created and announced due to popular request to be able to use a spindle on the Onefinity CNC.


Got it thanks so much for the info

Hi Bill,

Would you mind sharing the feeds/speeds that are working for you regarding the 1/2" diameter bits?
I just recently purchased a few but was unsure about the parameters. I have an up-cut and down-cut end mill in addition to a ball nose. I most frequently work with hardwoods. Thanks!

I only went .25" deep for a juice groove using my 1/2" ball nose and I don’t have a saved file where I used my 3/8" end mill. However, I just allowed the feed rate that was given from Amana in the tool catalog. Below is a screenshot of the 1/2" ball nose. Just be sure the piece is VERY secure or the force will move the work piece!


Thanks for your help!