Bit Noise, Amana XL bits and general advice needed

[JP_36]

Hello all. Over the past few weeks i’ve been able to start my CAM journey. I have the woodworker PRO, use Fusion 360 and a cabinet that allows me to cut deeper stock. Anyway, I typically am routing larger wood bodies (13"x6") for lamps and other work. And this was my first go around with my lamp design (can we not attach images?). I use the Makita Router currently, and bought a few Amana 4" XL bits (46590 & 46490). Does anyone have any experience/tips for using these XL bits?
The first thing I noticed when running some test cuts, is they generate a lot of noise. When the full cutting tip was engaged, it sounded like it was bogging down - maybe rubbing. I tried the bit at the recommended 220ipm, and various other feed rates down to about 140. Also adjusted the RPM’s (from 18000 to 14000, per recommended chip load), but it still sounded like the tip was bogging down. My solution was to change the bit info in the tool library so that the CNC only used the bottom .25" of the bit to cut. This eliminated the noise, and the cut was much cleaner. Wondering if anyone has any advice on this?
Does it sound like the issue, was indeed, the bit being too engaged in the wood? I know that vibration increases with these longer bits also - perhaps the issue?
Also, would I be able to engage more of the flutes on the bit using a spindle as opposed to a router? I need the extra length for my designs, and I’m presuming that they were not meant to be used with a router - but I could be wrong.

2. another issue that came up is that Fusion 360 did not stop the router when the tool change was required. It just went to the next operation. Anyone have a fix for this?

I’d be open to anyone’s opinions regarding these bits (or longer bits in general) and how to better use them - router vs spindle - or anything related. I’m just ramping up my CAM experience, so open to all opinions.
Thank you,

[KenA (Ken)]

I think you already fixed it. Cutting more than 1/4” per pass isn’t something I’d do with a router. I never did more than 1/8”.

[Mitch]

I don’t have the Amana but I have a similar spetools bit. With that much stick out, I go between 1/8-1/4” depth of cut. For the finishing pass, I take no more than 20 thou width of cut. While I have a spindle now, I’ve done that in maple with my makita and not sure I’d do it differently with the spindle…too much stress on a 1/4” bit trying to do much depth and width at the same time. If it doesn’t break, the vibration will leave a horrible surface finish.

For #2, make separate tool paths for each bit. Somewhere in the forums I remember someone (probably @Aiph5u, he’s always got the answers or links!) a mod to the default 1F bit change routine. I haven’t implemented it since I separate every bit into its own file

[Echd]

Those deep cuts are asking a lot from your router. Go slow and much lower depth of cut.

[Aiph5u (Aiph5u (not affiliated with Onefinity))]

Hey Mitch, hey all,

@Mitch

For #2, make separate tool paths for each bit. Somewhere in the forums I remember someone (probably @Aiph5u, he’s always got the answers or links!) a mod to the default 1F bit change routine. I haven’t implemented it since I separate every bit into its own file

thank you! Yes, it’s here

[Aiph5u (Aiph5u (not affiliated with Onefinity))]

Hey JP_36,

the longer your bit is, the more it will be bent and induce chatter. You will have the least problems if you always use the shortest bit possible. So if you want to mill a deep pocket, I would start with a short bit and use the long bit only when you reach more depth. Also the diameter of the bit is important. Unnecessary to say that a 6.35 mm bit is a little thin for the crazy length. The longer the bit, the larger the diameter should be to prevent bending and chatter. I would use nothing under 8 mm (Makita is sold with 6 and 8 mm collets outside of North America).

@Aiph5u

there are different sizes of the proprietay Makita collets available here:

https://elairecorp.com/makitaroutercollets/

By the way, outside of USA, the standard Makita RT0702C comes with 6 mm and 8 mm collets. You can order them everywhere .

Also when milling wood, I would use a very high rotational speed (depending on number of flutes, I use a formula). And finally the depth of cut, the feed rate, and the stepover should correspond to what the hardness of the wood allows.

@Aiph5u

@Aiph5u

Ball nose cutter

Radius Mill Z2 Ø 8 mm UNI

Here this 8 mm diameter ball nose is available in XL = 101 mm (4"), overall length, but with 6 mm diameter it is only available with 76 mm (3") overall length, which makes sense to me (¼" = 6.35 mm, 8 mm = ≈5/16").

Sorotec Shop » Cutting Tools » Sorotec tools » Radius Mill » 2-Flute UNI » Radius Mill Z2 Ø 8 mm UNI

With a spindle with ER-20 collet, you could use up to 13 mm bit shanks (including half-inch bit shanks) and very long bits that will bend less.

[Aiph5u (Aiph5u (not affiliated with Onefinity))]

Hey JP_36,

(OT)

@JP_36

can we not attach images?

yes, you can!

• Understanding discourse.org Trust Levels

[TDA (John Torrez)]

Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.

Short version. These kinds of tools are made for finishing and cleanup work. I say this as someone that works for a company that makes versions of these. While many people try to use these for main cutting they just don’t perform well that way. you are much better off as Ailph5u said going with a bigger tool or shorter length of cut.

For those that want the more technical side. I’ll try to demonstrate it for a hopefully better understanding.

For this I’m going to be using Millalyzer (Link). This is mostly as it’s fairly easy to setup and easily available to anyone that wants it. I’m going to model something close to the 46590. So 1/4", 3 flute, 0.5" LoC, 0.235" neck to 2.75". I’m going to be using a “standard geometry” though for the rake, a 25° helix, and I’m choking the tool to the edge of the neck (2.75" stickout). For material I’m going to be using paper birch.

More caveats… While this helps to understand some of the issues there’s still a LOT of variables that this isn’t modeling. Additionally, I have an impossible machine programed to show what the tool would do more or less without influence of machine rigidity.

All that aside this is what we get with the recommended settings slotting.

You’ll see a few things highlighted here. The first thing to look at is tool stiffness over on the left. This is how much force it would take to move the cutter 0.001". In this case it’s only 1.85lbf. Below that you will see tolerance or how much it will move from the programed path with this load in a single rotation. With the recommended RPM and chipload from that Amana tool it’s 0.0119". Last we have power which is at 757W this is more than you will get out of the Makita router (routers are rated at peak draw).

Here’s what the prediction over 12 revs looks like.

In this case it exceeded 10% of the tool diameter so it stopped trying to calculate. Basically the tool shouldn’t be trying to do this. The physics don’t work out in it’s favor.

So lets change some of these numbers. I’m going to chop the RPM to 12K (resonance, surface speed, etc.), pass depth to 0.125", stepover to 0.0625", and reduced the chipload to 0.004".

This makes something calculatable and after the 12 revs we are at worse case of 0.0196" deflection in feed and 0.0123" in transverse. That is still a LOT of chatter.

Now let’s look at the same tool but with only 1" of neck and stickout.

Now it’s 33.93lbf for 0.001" deflection and a single rev is only off by 0.00054".

Here’s the same cut over 12 revs.

0.0004" feed and 0.0007" transverse deflection.

For the sake of apples to apples the long necked tool reduced cut.

0.0002" feed and 0.0001" transverse.

Final disclaimers on this. These number will change with the material cut, carbide grade, rake, helix, core, and bunch of other geometry options. I’m sure that Amana is doing at least some of those to make this less severe. You can only get so far with that though and physics is still a thing.

Hope that helps to understand some of the issues. Let me know if there’s something I can help with.