3/8 bit feed rate/ depth per pass reassurance


Have a new bit and I think I’m being a little chicken with my cut settings. I have a 3/8" round nose bit, 1/4" shank. All I need is three straight lines down some heavy pine. I’m using 30 in/min feed rate, 9 in/min plunge rate, 0.028 in depth per pass. Dewalt 611 set on speed 1.

Looking at this I feel I need to make changes.

I really don’t want/need to cut 0.375 per pass but could I ? Would anyone like to suggest a few settings to stay in a comfortable zone? I would just like a little faster than what I’m doing without pushing anything.

Thank you in advance.

I don’t use easel, so take this for what it’s worth. I use 1/4" diameter straight, 1/2’ diameter straight, and 1/2" roundnose bits most of the time. In one machine I have which has mach3 and anti backlash screws, I usually run it no more than 50 IPM.

On the Xcarve, which has the 9mm belts, I’m able to increase the speeds. Depth of cut varies, but I usually go about 1/8" deep at a minimum. I wouldn’t go .375 deep in one pass, but probably would do it in two passes. Pine would obviously respond differently than maple.

Try a piece of scrap first and see how the machine responds.
This maple and I think I went in .125 deep cuts :slight_smile:

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Thank you. Through multiple slow trials I was able to increase it to 42 IMP with 0.125 deep. That seemed to give me tiny chips instead of the dust storm I was creating.

I’m very hesitant to make these setting changes as the whole machine is brand new and I really have no clue what I’m doing, just kind of reading and winging it. I have a few 1/4" 2 flute downcuts that I should probably ask about too. I’ve been running them at 30 IMP and .06 deep. Not cheap bits to be wearing out as I need the extra long ones.

You are unlikely to damage the machine by pushing too hard (the motors just aren’t strong enough to break anything. You’d most likely snap a bit/destroy your work. If you upgrade the motors to much more powerful steppers and beefier belts (as I am in the middle of doing) you can put much more mechanical strain on the machine components (but even so the bit is the weakest point). On my Tormach which has ball-screws end of belts I’ve snapped my share by crashing into the work piece.

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I don’t think I will be upgrading motors anytime soon but I’d like to think someday I may love it enough to consider it. I’m just watching a lot of things. I’m pushing the limit of height clearance on most of my projects. The bracket that holds the router can’t even clear the clamps I’m using. Hence my cut settings hesitation. I just don’t want anything going wrong when the bit is 1 1/2" deep in a project and my clearance going around is so limited.

I’d love to just do the math for the cut settings but it seems I have so many unknown or variables in the equations. While I pretty much understand the depth per pass I don’t really understand how to calculate the feed rates. It seems so many just hit the increase button until it feels right. Nothing feels right to me. It feels like a toddler running around with a scalpel and I’m just waiting for a tantrum.

I can only speak for myself , but I don’t calculate any feed rates. I watch what’s going on with the wood and the results. You can hear and see whether you can go faster or need to slow down. It’s getting familiar with your machine. You have seen you can go faster and that’s part of the learning curve. I think a shallower depth of cut per pass would allow more speed and visa versa, and the bit diameter and quality impacts that too. A small cheap bit won’t allow things to go deep or fast as compared to a larger diameter Whiteside router bit ( or similar quality).

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The goal parameter in feedrate is how thick a slice (Chip Thickness, Ct) do each flute of the bit slice per revolution. This parameter is often stated for branded bits. Say you use a 1F 1/4" bit in wood and Ct target is 0.01" (Playing with arbitrary numbers)
The bit is also 1flute (1F) so there is only one Ct per revolution.

Then we need RPM, the Dewalt minimum (and preferred) RPM = 16000

RPM * Ct * Flutes = feed rate
16000 * 0.01 * 1 = 160inch per minute (ipm)
A 2flute bit = 320ipm

However, the rigidity of the machine is what ultimately determine proper Ct and Chip Load (Ct+depth)
Going shallow give you a larger envelope to work within in terms of rpm/feed rate so if in doubt go shallow first.

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Exactly the reason I posted.

I’m running this machine around at 30 IPM and my calculations are coming up more than 5 times that.
This is the bit I use the most. https://www.toolstoday.com/v-14076-46421-k.html
So 16000 * 0.005 * 2 = 160
So we are saying I’m going 5 times slower than I could/should be? My husband will have my head if I start shooting wood across the shop.

That ultimately depend entirely on the machine rigidity, and most bit makers assume a professional grade (very rigid) machine for those numbers.
Chip thickness (and even thickness) is highly affected by any chatter/tool motion and is the prime source for bit breakage.

The minimum RPM of the Dewalt is for many projects a little on the high side.

Your safeguard is restriction of depth per pass, start shallow and increase incrementally untill you start to hear/feel the machine struggling. It will be some trial and error.