Endmill failure or wrong feeds and speeds?

[Lee Roberts]

With the bit screaming as you suggest which setting would you have adjusted? I'm guessing you would have adjusted the RPM down? I would have probably been tempted to reduce the feed rate. I probably need to practice different settings on a scrap piece of wood to get a better feel for it.

Yes mate I did, It's a great machine that Dean and Jared made for me. Really pleased with it.

I'm not sure but the main point is you shouldn't need to guess at any of it, as long as you maintain the known good chip size as you change the feeds and speeds, then everything should to go plan for you, what CAD/CAM software are you using ?

[CNCOlly]

I used Vectric Aspire for this project.

The penny has just dropped with regard to chip load after your last comment. Chip load and chip size are interchangeable terms. I didn't actually realise that the chip load meant the size of the chip coming off the tool, I don't really know what I thought the chip load value related to. Hopefully, that will help thanks.

[Lee Roberts]

Evening Oli,

Well chip load also known as the Feed Per Tooth is actually supposed to mean the length of material being loaded into each cutting edge, so there can be a difference because you could argue for all the dimensions of a chip: width, length, thickness etc., so chip load is really referring to the length of the chip...

It is to be known as the theoretical length however, as other things like the width of the cut and/or flute edge geometry affect the thickness of a chip. If you measure the thickness of said chip accurately, the thickness you read wont give you the same numbers as the original chip load that was calculated.

Personally I think calling it chip size generalises it and makes it a simpler thing, in the beginning I did the same as you and didnt really give it enough thought so also didnt really know what "chip load" meant, I jumped straight to a basic speeds and feeds chart with no pictures etc, I quickly worked it out from there and since I've always called it chip size to myself and when explaining to people...

We both learnt something from this today, I did underline all of the instances where I called it chip size in my other post, on the assumption that you and others would notice that and get it, however I realise now I should have just made it clearer, sorry about that.

Have you tried cutting MDF yet?, reason I ask is because not many people realise (me included) that if you get the formula right for cutting MDF, it too will produce proper chips, I was really surprised by that and always thought of MDF as a dust only kind of thing to be working with, its quite a good material to learn and "chase" the correct chip on...

[CNCOlly]

Evening,

All the MDF I've cut so far has just made dust. I've got plenty of offcuts of MDF so probably worth using some of it up to try and get some chips. I think MDF can vary in quality quite a lot? I'd like to give it a go over the next few weeks and might report back with my findings to share my learning experience.

Oli

[Lee Roberts]

Hi Oli,

Yea when you hit that sweet spot with MDF you will definitely know, if you go with any of the "pro" type from any of the top brands you should be good, the cheap stuff from the likes of B'n'Q etc is no good, though they are doing Medite Trade, particularly in the 18mm, again this doesn't machine as good, I would say to anyone go with Medite Premier if you can get it in, otherwise the likes of Build Base and/or Selco do Norbord / Caberwood and this is good enough, again stay off the Trade line with these too.

Ok cool, I'll try and grab some shots of my edge finish for you and maybe a video.

[CNCOlly]

Quick update. I got back from holiday midweek and on my return, I received a package containing some new endmills from XCAN - Aliexpress. All excited and stocked up on some lovely new oak boards from the local hardwood supplier I decided to have another go. I snapped the new endmill on my first attempt... I'm clearly driving these things way too hard. Time to take a step back and slow things down. Is there a way to tell if the endmill is actually solid carbide as advertised? Ideally, so I can rule out the chance of it being a low-quality bit. It certainly looks the part. It failed on a plunge almost at the end of cutting two parts out. Unfortunately no video.

Here are my settings, again I thought I was being conservative with the settings 1/2 the chip load that the endmill of this size is supposed to be able to cut hardwood.




Some pics of the fail.

[Lee Roberts]

I'd say the plunge feed rate was to much, if your going to plunge with a tool designed for side cutting, its best to ramp into the cut if you can or use a drill operation first to open it up for the cutter to fit inside and then start side cutting. Or you can use a spiral ramp cut, did you use either of those or just plunge straight down into the oak?

Edit:
Is the second pic where the cutter broke in the oak?, it looks like it is and suggests a straight plunge...