There is a vast array of small yet important decisions that must be made when working in CNC machining. For example, it is vital to choose the right number of flutes on end mills to enable your tooling to ensure smooth operation and maximize productivity. Your best option will depend on a number of factors, including the hardness of the materials you are looking to cut as well as the parameters of the tooling at your disposal.

It’s frustrating to see SRAM highlighting the ability to change chainrings on the new Red XPLR AXS power meter as an exciting new feature, given it was SRAM that took away that ability in the first place.

For a start, you’ll need SRAM’s proprietary tool (the SRAM Thread Mount Chainring Removal Tool) to remove and install a chainring, which costs £63 / $65 / €70 and can only be used for this one job.

That’s fine if you’re a tool fetishist like Oscar Huckle, but it can also just feel as though riders are being squeezed for yet more of their hard-earned cash.

It’s not as if Quarq power meters have always had this limitation. Prior to the launch of SRAM’s first AXS groupset (SRAM Red eTap AXS), the brand’s Red Quarq DZero power meter featured a five-bolt 110 BCD pattern with – you guessed it – interchangeable chainrings.

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I’m all for innovations that make our lives or rides better – heck, I even believe press-fit bottom brackets are better than threaded ones. But if an ‘upgrade’ or new feature doesn’t offer any tangible benefits then it’s fair to ask what the point of it is, and what was wrong with the old way of doing things.

Meanwhile, 4-flute end mills have been preferred when machining steel and similarly hard alloys since they have more cutting surfaces to contact the part per rotation. Since such harder metals require a slower feed, using end mills with 4 or more flutes serves to increase the rate of metal removal.

Shimano cranksets all use bolt-on chainrings, though, and don’t seem to suffer any reduction in front shifting speed or accuracy as a result. In fact, many – myself included – regard Shimano’s front shifting performance as class-leading.

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For SRAM Red XPLR AXS, that means only five 1x chainring options from 38 to 46t (in 2t increments), with no third-party or 2x options as things stand.

The problem, however, is the performance gains are intangibly small compared to what you lose – namely, the ability to replace chainrings, either for wear-related reasons or because you want to change your gear ratios.

With the launch of its new Red XPLR AXS gravel groupset, SRAM has finally brought its Thread Mount chainring design to a non-MTB power meter spider.

On paper, it looks as if it solves the problem, but in reality, its proprietary nature introduces another set of issues.

I also bristle at the idea of a brand taking something away from riders, only to add it back in later as a ‘feature’ – especially when the ‘new’ system is less functional than the one we already had.

While this likely won’t trouble many owners of the new 13-speed groupset, it means the new Red XPLR AXS power meter can’t be adapted easily for use on a road or time trial bike, or repurposed to work with a non-SRAM groupset, for example.

End mills with higher counts of 5, 6, and 7 flutes are increasingly being used to cut harder materials, as a higher flute count allows for a tool with more strength and less wear, resulting in a longer tool life. High flute counts can also be beneficial in specialty applications when dealing with certain kinds of ferrous materials.

Thread Mount debuted on SRAM’s T-Type Eagle Transmission groupset, where you might think it was introduced due to the space limitations enforced by the smaller chainrings mountain bikes typically use (a smaller chainring necessitates a smaller BCD, which leaves less room for electronics in a power meter spider).

It has always felt a shame, therefore, that the high-end Red AXS and Force AXS power meters featured such an annoying flaw.

That wasn’t the case, though. The smallest chainring size available for the XX SL Eagle AXS Transmission power meter – 32t – is the same size as was available for SRAM’s previous XX1 Eagle power meter, which had a four-bolt 104 BCD with interchangeable chainrings.

In theory, this solves one of my biggest peeves about SRAM’s recent power meter spider designs – namely that, on its Red AXS and Force AXS power meters, the chainrings are integrated into the spider with no way to remove them.

As with the tool, I can see the potential benefits to SRAM here (it might sell more power meters if you need to buy a specific one for every type of bike you own) but the benefits for riders aren’t so obvious.

Other brands have also shown it’s possible to create stiff chainrings and have excellent front shifting without needing to resort to impractical integrated designs.

To recap, more flutes on end mills means more strength and a smoother finish. However, lighter metals may require a lower flute count to be sure that any chips have space to clear during operation.

There are the threaded inserts on the outer chainring to consider too, but even so, we’re only talking about a few grams at worst.

Optimal flute count also depends upon the specific machining application in question. End mills with high flute counts work well in finishing applications since smaller amounts of material will be removed and chip evacuation will not be a primary concern. On the other hand, roughing operations will benefit from a lower flute count, where it is necessary to have larger flute valley to evacuate chips with increased frequency.

Its previous-generation Force eTap AXS power meter (the PM-FRC-D1) featured hidden chainring bolts, and its AXS Power Meter Spider (the PM-AXS-SPDR-D1) almost ticks every box, except for the fact it uses a non-standard four-bolt 107 BCD, which significantly reduces its chainring compatibility.

Perhaps most obviously, though, while you can change chainrings, you’re stuck with only using SRAM’s own Thread Mount options.

If you have any questions or would like advice regarding the appropriate number of flutes for your end mills, please feel free to get in touch with us at Star Tool Inc today. We currently provide carbide end mills of anywhere between 2 to 7 flutes and are prepared to help you find the perfect carbide end mill solution for your metalworking needs.

However, adding more flutes is not without drawbacks, as the larger core takes up space and limits flute valleys that otherwise allow chips to evacuate more easily while machining. As a result, stronger end mills with higher flute counts are better used when cutting harder, more ferrous material that require a faster rate of metal removal.

It's true that no bolts is lighter than four bolts, but the difference is miniscule – a set of four Shimano T30 chainring bolts weighs only 4.5g.

Most end mill flutes traditionally come in 2 or 4 flute variations. 2-flute end mills have generally been preferred when machining aluminum materials, since the extra space is necessary for the relatively larger chips to evacuate when the tool is operating at a faster feed.

To further prove the point, front shifting with a Quarq DFour DUB power meter (which is effectively the same as SRAM’s Red / Force AXS power meters but with a spider design that blends with interchangeable Shimano Dura-Ace R9100 chainrings) is also fantastic.

Perhaps weight weenies will disagree, but unless you’re building a bike to win the UK national hill climb championships, I think every bike can afford an additional 10-20g to accommodate interchangeable chainrings.

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Just as standard bottle cages are perfect as they are, so is the practice of using standard fasteners to attach consumable parts such as chainrings.

Yet, while I’m glad SRAM has adopted this design with its latest gravel groupset, let’s not break out the champagne and declare this issue a thing of the past.

Of course, there’s no perfect power meter that can be used on all bikes and for all disciplines, but in this case the limitation isn’t inherent to power meter spiders in general – it’s something SRAM has designed in by choice.

Instead, SRAM says Thread Mount simply enabled it to “reduce weight without compromising reliability”. As already discussed, though, the weight savings are so negligible it isn’t worth it.

Thread Mount is a slicker-looking design compared to exposed chainring bolts, which is important for high-end products. But hiding the chainring bolts, as Shimano does on its HollowGlide chainrings, achieves a similar effect without any loss of functionality.

Taken on their own merits, both of these things are true – chainring stiffness plays a role in front shifting performance, and getting rid of the bolts and threaded inserts will save some weight.

With Thread Mount, SRAM effectively says riders get the best of both worlds – the lower weight of ditching bolts, plus the ability to change chainrings.

The general correlation between flute count, core size and tool strength is straightforward. More flutes equals a larger core equals greater tool strength. Furthermore, end mills with higher flute counts tend to have a smaller cut depth and so can be used to provide a smoother finish on virtually any material.

SRAM’s argument for integrating the chainrings directly into the power meter spiders was that it made for a stiffer system (which improves front shifting) and lower weight.

I distinctly remember the first time I tried a Shimano HollowGlide outer chainring (on an Ultegra 6700 groupset), for example, and the improvement compared to traditional chainrings.

Today, it is also possible to order end mills with 3, 5, 6 or even 7 flutes. 3-flute carbide end mills have gained popularity when cutting aluminum or non-ferrous materials, offering superior productivity and finish as compared to traditional 2-flute end mills without obstructing chip evacuation.