# Half-inch bit limitations

**URL:** <https://forum.onefinitycnc.com/t/half-inch-bit-limitations/19031>\
**Category:** Elite Series (Masso & Redline) (Gen 1)\
**Created:** [February 25, 2023, 6:31pm UTC](https://forum.onefinitycnc.com/t/half-inch-bit-limitations/19031 "2023-02-25T18:31:29Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![349iq2345](https://avatars.discourse-cdn.com/v4/letter/3/bb73d2/32.png) [@349iq2345](https://forum.onefinitycnc.com/u/349iq2345)\
**Post date:** [February 25, 2023, 6:55pm UTC](https://forum.onefinitycnc.com/t/half-inch-bit-limitations/19031/3 "2023-02-25T18:55:41Z")

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Hey Tobias,

> [@boxer](#):
>
> 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?

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** :

![f704eb_d7ced3cfde53458a838f96688847d9e5~mv2](https://us1.discourse-cdn.com/flex022/uploads/onefinitycnc/original/3X/a/a/aacced0efdf364b4895aa76991f69638983eee07.png)  
Image: [Onefinity 80 mm spindle mount](https://www.onefinitycnc.com/product-page/80mm-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](https://forum.onefinitycnc.com/t/80mm-mount-upper-z-limit/10692/2), the Z axis travel is 133 mm.

Most CNC mills have **two linear bearings per rail** , as can be seen [here](https://forum.onefinitycnc.com/t/universal-z-axis-assembly/4415/13), [here (RoverCNC)](https://www.rovercnc.com/collections/z-axis-collection/products/rovercnc-z-axis-assembly-200mm-stroke-7-87?variant=53751165333), or [here (Sorotec Alu-Line)](https://www.sorotec.de/shop/DIY-Kit-Z-Axis-Alu-Line.html).

Users thought of [mounting two 80 mm mounts on top of the other](https://forum.onefinitycnc.com/t/z-axis-rigidity/10732) or to simply mount an [Universal Z assembly](https://forum.onefinitycnc.com/t/universal-z-axis-assembly/4415). 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](https://forum.onefinitycnc.com/t/introducing-the-z-20-heavy-duty-z-slider/16622/1)** 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](https://forum.onefinitycnc.com/t/7-31-2020-update-z-slider-upgrade-for-all-outdated-as-of-2020/473/39) with 16 mm shafts, but the spindle mount still runs with only one, however bigger, linear bearing per rail.

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