bits

[mchurchf]

I have a couple questions that i can't find discussed on this forum.

What is the difference between an endmill and a straight edge bit? Do both bits do the same?

Why would I need a regular endmill bit if I have a ball nose bit? Will a ball nose bit cut and smooth the surface? Or should I use an endmill then go over it again with a ballnose to get a smooth surface? Confusing!!!! lol

Thanks guys, as you can tell I'm newbie

[jeb2cav]

Hi,

If I understand your question - many 'straight bits' (I'm thinking they might also be called edge bits) are primarily designed to cut along the edge of material. The cut on the 'bottom' of the bit may not be as smooth as needed for example for a cnc pocket toolpath operation. End mills are designed to cut along the length or long part of the bit, as well as the bottom.

If the surface you are cutting is flat, you will always get a better result using an end mill vice a ball nose. There may be some other opinions on this. The other big advantage in using an end mill for an operation like this is time. It will take considerably less time for you to carve a flat pocket using an end mill than a ball nose.

[mchurchf]

Thanks jebcV, Lots to learn. I bought a small set of bits from Rockler which I should be able to use on my router table. Maybe being frugal isn't the right decision.

[Eagle55]

I good thing to always keep in the back of your mind is that you absolutely have to have bits that are designed for plunging. Not all carbide tipped blades are. Take for instance a rabbeting bit. You can cut a rabbet with a flat side and flat bottom just fine when you are feeding it from the side (where the cutting tips are) but if you were to take that same bit and plunge down from above it would cut where the carbide tips are but not on the center axis of the bit. (It would hit non-cutting areas towards the center of the bit where the ball bearing would normally be. So when choosing bits always live by the saying... if you can't plunge, you can't shark. (ok, so not a well known saying cause I just made it up LOL) All those considerations aside, Joe is correct in that it would take much longer to clear an area with a ball nose bit because your step over amount to make it flat would be about 8% and you would still have little ridges, where you could step over with an end mill or straight edge bit at about 40% and have a flat bottom as opposed to a radius cut. If you slow your feed rate down you can usually get a smooth cut with minimal sanding needed. Of course the sharper the bit, the better. I have actually had smoother cuts in Corian using a straight flute bit over a spiral edged bit but I think that is mainly because it is a size that I don't use that much and it is sharper. I think my 1/4" end mill used to cut a little bit better when it was new, although it is still sharp enough use. Something else you might consider is to use a core bit with a partial flat area and edges that round up with a radius. I bought some round nose and core type round nose for manually routing signs with templates, before I bought the Shark. I never used them till I had the Shark but they were "Plunge" type designs so I had additional bits for the shark. Also endmill designs have a spiral to the cutting flutes which theoretically can work with you or against you. UP spiral can help remove wood chips out of your cut but can leave a ragged top edge on your material depending on type of wood. DOWN spiral can leave a better top edge but pushes the chips down into your cut which can be a problem (but rarely is in my real life experience). The router fan usually blows most of the chips and dust out of the cuts regardless of the bit design.

Also for consideration, feed rates play a lot bigger part than most people give it credit for. Even though a bit may be capable of cutting a smooth bottom, if you have feed rates that are high enough that it creates a torquing pressure on the gantry you are going to, in essence, be flexing the gantry and changing the elevation of the bit without changing Z position at all. This can create all kinds of problems but among them are a rough surface in a pocket cut. Just because the machine can travel at many speeds doesn't mean that you can successfully cut at all those speeds. Sometimes the desire to do something quickly can have perilous results in the quality of a project. Hope these answer are along the lines that you were looking for. I agree Joe's previous statements. I just have the disease of talking more to say the same thing. LOL

Roger

[mchurchf]

Thanks again guys, really good and helpful information. I haven't been able to cut anything that I have been happy with but it'll get there. The good thing is I'm getting some good firewood for next winter.