I get the feeling the shops on campus are behind the times then...always use center drills to start a hole (all our drills are HSS).

Spot drillbit

I haven't used one in years... You shouldn't center drill or spot drill for that matter prior to running solid carbide drills. We use spot drills for chamfering holes and contours.

Feb 17, 2024 — Another vote for Yonico. Decent bits at a decent price. I usually buy premium bits but for a limited use bit I have had good luck with the ...

Ok I'll start the controversy. With the understanding that the split point carb/short hss drills don't need the starting hole we have found here that the center drill is the more accurate spotting tool. The trick for holding the accuracy is NOT to use the same tool for chamfering. If your drill/reaming a 3/32" hole then use a No.0 center drill but only drill it to the chamfer. The idea is to keep the starting dia just barely bigger the the chisel edge/web of the drill. If the chamfer of the starting hole is bigger than the drill dia there is a tendency for the drill to pull. With the center drill starting dia into the part to the center chamfer there is also a guide to help hold the location.

I use several Whiteside 2 flute up and down 1/4" bits and they work great but the side flutes cut as well as the bottom flutes.

Great Thread! My question is this, I'm drilling a .052 hole with a solid carbide drill and this hole has a pretty tight tolerance. If I can get a .053 gage pin in the hole the part is junk. How should I be starting the hole? With a small spot or center or nothing at all?

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I’ve used a router for years; even made my own Norm Abram router table. Have also used TurboCAD to help me create some of the stuff I’ve made. But I’m stumped with one particular thing that’s critical to using my Shapeoko Pro. Do the edges of the bits cut like a conventional router bit, or are the flute just for chip evacuation?

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I've had good luck using Vermont Tool's "spott". It is a one insert indexable spot drill with a 144 degree included angle. That way it will nicely nest the point of any drill 140 degrees or less. This tool elimanates the need for resharpening so they repeat well. In most steels I run them at 1800 rpm .001. inch per rev. They can give you up to a .7 dia. chamfer. I use center drills mostly for shaft work where there are subsequent grinding operations.

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Sure do... Not sure how HSS would work, but solid carbide works great in 400 grade stainless. To be quite honest with you we use Harvey's carbide drill/end mill as our spot drills/smaller chamfer tools. The price is very good and you could drill (NOT steel) chamfer and mill all with the same tool. Works great on blending walls with chamfers.

Center drillSizes

For best reesults your spot drill should have a equal or greater angle than your drill and if practical an equal or greater diameter.

stronger cross-section than a center drill will produce a spot for your drill in less time with more accuracy than a centerdrill due to it's increased rigidity. and to me they are much easier to program with respect to the size chamfer on the hole after drilling and tapping.

The v7 CC has a new keyhole tool path that you have to cut the full depth of the keyhole and then plow forward for the smaller diameter but this is a special toolpath. Using bits that cut the full depth of a slot are very hard on 1.25 HP routers and on the belt driven Shapeoko’s. That is why most bits only cut a few thousands per depth of cut so compensate for the lack of power in trim routers. With more powerful routers and spindles you can cut deeper but you are still limited by the limitations of belt driven cnc systems. Even the Pro and HDM have limitations of depth of cut although they have greater power to move forward there are limits to cutting aggressively. When you go to industrial type cnc machines they can plow through wood and metal much easier because of the horse power they have the robust nature of their rails and bearings. Even on a table router you should never exceed 1/2 the diameter of the bit in the plunge or you can burn wood and/or bog the router down. A 2-3 horse power router has your human horse power pushing them along but the horse power of the router motor is still the limiting factor.

Routers used for manual work work exactly like the cnc router bits. Think about cutting a 1/4" slot on a router table. Yes the bottom flutes cut but so do the side flutes. If the router bits did not cut on the sides you could never cut a slot. As Michael said drill bits do their cutting at the bottom and the flutes only extract the chips but drills are not the same as router bits. The only cutting in a drill bit is at the bottom because as they cut down the hole is already cut and you only need to evacuate the chips. Router bits from your router table will work in a cnc except for bits with bearings. It is never a good idea to use bearing type bits in a cnc. The reason is because they cannot plunge and while cutting eventually you get to the bottom. People do use bowl bits that are curved at the bottom on their CNC for a round bottom or for cutting juice grooves on cutting boards. You can use core bits but if they have bearings try to avoid them because of the depth of cut issues you can run into.

Apr 26, 2016 — These bits cut smoother than other straight bits because of the precise shear and hook angles. End of bit relief allows for fast plunging.

Spot drillangle

note: for best accuracy when gun drilling often the hole is spotted to the same diameter as the drill but sub flush leaving a guide bushing in the part.

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I use harvey on a daily basis. The quality on everything they offer is amazing. I would recomend to anyone. I use the thread mill in titanium and I have not found anything that lasts longer.

Spot drill vs center drillsize

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When you set up a custom tool you can set the depth of cut per pass. So either set it to the full depth and set the depth of cut to the same as the full depth. You could say you want a 1/4 round over set the depth of cut to 1/8" and set the depth to 1/4" so it will make two passes. You can make the passes smaller depth and just hit pause and stop when the round over looks good.The trick is to set the offset so you get the round over the correct distance from the edge. Do not use router bits with a bearing at the bottom. That could cause your router to stall if it hits a corner because the bearing cannot cut just the router bit. If you only have bearing roundover bits you can take the bearing off for the use on the cnc.

Spot drill vs center drillreddit

Often in a production environment a 45 deg spotter will create the chamfer and guide the drill sufficiently saving a tool change. Worhs best with stub drills.

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Center drillangle

The short rigid spot drill resists the tendancy to wander. The drill then contacts first at the tip and follows the spot location providing the best positional accuracy.

I am actually with Tim to some extent on this. For precision work, I prefer center drill (no chamfer tip only) then drill. I prep the hole with a separate c'sink as required.

Twistdrill

If you listen to a drill entering the hole left by a (lathe) center drill the nasty growling sound is the result of the external portion of the drill contacting first and jumping around. Bellmouth holes, drill damage, and loss of c/l position result especially when the surface is at an angle as in castings.

Is the concept not the same? Have a short, stubby, rigid tool to start a straight hole such that a longer drill can follow it straight?

Center drills are exactly that. They are for making centers. The smaller diameter tends to break off in the part during production use. This is not desireable.

Not to highjack this thread but since you mentioned Harvey(a big +1 to their spot/drill/chamfer tool) have you tried any of their thread mill cutters. Seem really cheap. I've been paying almost 3x what they are getting. Just wonderin.

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If the surface drilled is not perpendicular to the hole it is essential that the spot drill diameter is at least that of the drill.

Spot drillsizes

Whats the difference here. I'm well aware of what a center drill is and what its used for, but in some thread a while back regarding reaming holes someone was talking about how center drills weren't reliable enough.

I haven't tried them yet, but if they're as good as most of the other stuff they have than I will have to. This is the 1st time I actualy looked at their thread mills and they are very inexpensive... Now if only they could do a little better on the LOC for them.

Outside of some specialty bits for the CNC (which are essentially high speed drill bits), you can assume the CNC bits will cut when moved horizontally into the material. So, for CNC bits the flutes are cutting edges.

Apr 7, 2012 — Basically the same way as a two start thread on a manual where you move the compound slide 1.5mm but set the machine to thread at 3.0mm pitch.

Not all CNC bits are made for plunging - there are some that should only be used to cut horizontally. You’re unlikely to run into one like this though unless you are looking for a specialty bit.

Hey Will: I’ve never tried my router table bits, so, if I want to do a 1/4" or 1/2" round over on a rectangular frame I’m assuming I do the setup on the line or maybe with a small offset - however, how do you calculate/set the depth of cut because most of those do not go to a center point. I may have something coming up that I would like to try that on rather than going over to my router table to do the job manually.