drilling out plasma holes

[atomicjoe23]

If you are referring to my post for some/all of these questions here are my answers:


What thickness parts are you getting flame cut?

Varies, anywhere between 1/4" to 3".

Have you had these parts plasma'd before and had the same results when drilling?

We have recieved stock laser-cut, plasma-cut, water-jetted and/or EDM'd out.

What size are these holes before drilling and what size are you drilling to?

We generally don't have the holes pre-pierced for holes when we get them, we are generally having plate cut into various shapes then we machine the rest of the features in. . .having the main shape cut out by another method other than machining is more of a time-saving, waste reduction, or money-saving thing than anything else. I don't work in an off-road shop though. . .I work in a toolmaker's shop so the work I do is quite a bit different than what the OP is doing.

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[socalmoto]

I have been using my cnc plasma table for a year or so now and have drilled out numerous plasma cut holes with cheap HF HSS drills. Infact I have not thrown away any bits out of my 8+ year old HF drill bit set due to drilling plasma cut holes. I primarily cut CR and P&O steel from .040 - .375. The key to saving bits is to use a slow spindle RPM, let the drill do the cutting, USE CUTTING FLUID, and make sure the cutting tip is sharp.

Yes i am cutting all mild and generally always use oil and my spindle speed is slow (down around 150rpm if i did math right with the pulleys). The first hf bit i bought i ruined by not cleaning the up around the plasma hole with a flapper wheel (which i always do now) and i didnt oil it enough because i was in a rush to knock out a lot of holes, but i wont make that mistake again since ruined tools take WAY more time. I still use that bit today since only one step was ruined....but ALL the new hf step bits seem to be complete garbage. I think the Ti plating is far thinner and no matter how slow and how much oil i use, they still will burn through and ruin the bit, and ive tried to sharpen the edge on a few of the newer ones, but once you get through the Ti, they wont last more than a couple plasma holes.

Try this. . .it is supposed to be cobalt HSS so it should last, but I haven't used it so I'm not gonna promise anything. . .
http://www.use-enco.com/CGI/INSRIT?P...PARTPG=INLMK32

That is the step i ended up going with and it works well so far. It cuts slightly smoother/faster than the hf (could be my perseption) but im more interested in how long it lasts and hopefully i wont have anything to post on it for years. I did try a friends rotobroach and i was impressed with the speed it can cut, but honestly i still like how much faster and easier the step bits are. Like i said, any hole size is the same bit and it makes a very nice deburred edge with no extra time.

[bigkell5]

I only use step bits on stuff under .060. I have never attempted drilling plasma cut holes with a step bit or resharpening them. I use the Titanium Nitride Coated Drill Bit Set for plasma'd holes under 1/2" and regular HSS for anything over that. Step bits kinda annoy me cause you have to plunge so deep to get to the bigger sizes. And how would you sharpen one of those anyway?

Let us know how that new step bit holds up after you get a bunch of holes through it.

[atomicjoe23]

I think the Ti plating is far thinner and no matter how slow and how much oil i use, they still will burn through and ruin the bit, and ive tried to sharpen the edge on a few of the newer ones, but once you get through the Ti, they wont last more than a couple plasma holes.

That statement leads me to believe that either the steel or the heat treat process used when making the bits has changed. . .they are either using inferior steel or the heat treatment (more than likely the final temper, but the initial austenization temperature could be too low as well).

That is the step i ended up going with and it works well so far. It cuts slightly smoother/faster than the hf (could be my perseption) but im more interested in how long it lasts and hopefully i wont have anything to post on it for years. I did try a friends rotobroach and i was impressed with the speed it can cut, but honestly i still like how much faster and easier the step bits are. Like i said, any hole size is the same bit and it makes a very nice deburred edge with no extra time.

I am glad that it's working out for you. . .if the steel is good (hopefully it is, but they didn't say which cobalt steel they are using) then it should last you a very long time!

I only use step bits on stuff under .060. I have never attempted drilling plasma cut holes with a step bit or resharpening them. I use the Titanium Nitride Coated Drill Bit Set for plasma'd holes under 1/2" and regular HSS for anything over that. Step bits kinda annoy me cause you have to plunge so deep to get to the bigger sizes. And how would you sharpen one of those anyway?

Let us know how that new step bit holds up after you get a bunch of holes through it.

If you are using a step drill that is constructed like this:



then you can either stone/hone the flat face that is actually doing the cutting if the bit isn't damaged and only needs re-sharpened. . .if the bit is damaged then you will need to regrind that face. Regrinding the face isn't necessarily difficult, but you want to remove only a minimal amount of material (only a couple of thousandths, .001"-.005", if possible). Removing too much material will negatively affect the performance of the bit. . .removing too much material could get you too far back into the radial relief area and the bit may then rub in areas that it wouldn't have before rather than cut. If you remove (grind) the material too quickly you could overheat the material and further temper the bit resulting in a softer bit that either won't cut at all or which won't last very long. If you do attempt to grind the bit you should try to keep the angle of the face relative to the centerline of the bit what it originally was. Obviously this is much easier to do in a shop with a dedicated tool cutter grinder, but with some patience, a steady hand and/or a well thought out sharpening jig you could re-sharpen a damaged bit with a dremel tool; it would be difficult to do this with a bench grinder because fo the size of the wheel. . .there just isn't enough relief between the wheel and the bit to try and sharpen the bit without removing material from an area you didn't want to.

Here is a picture that shows the actual cutting edge better. . .the upper edge is the cutting edge.



If you have a bit like the picture below, then it is going to be a lot more difficult to grind, but stoning it won't really be any more difficult.



This would all make a lot more sense in person and if I can post some pictures up later to help I will.

[bigkell5]

I guess i should have rephrased my comment. I understand how you would do it but seems like a PITA and you could mess it up easily if you don't know what your doing. a burr king may be good for attemping this. I don't see how taking off .005 could sharpen it to new standards though.

Those spiral cut step bits look cool. Do they hold up any longer/cut easier?

[atomicjoe23]

OK. . .here goes. . .

. . .just to make sure we are on the same page, you need to stone/hone/grind the flat cutout portion of the bit not the outside diameter.

Trust me, I sharpen all sorts of cutters almost everyday at work. . .even as a little as .0001" (yep, one ten thousandth of an inch) removal of material can change a dull cutter into a sharp cutter, it all just depends on how dull the tool has been allowed to get (read, how far back do you have to remove material to restore the geometry of the cutter). It is a lot easier to stop every now and then and stone an edge for 30 seconds to sharpen a cutter than it is to go spend a couple minutes at the grinding wheel or tool cutter grinder resharpening and re-establishing correct cutter geometry.

If you only need to stone the face to resharpen the bit it should only take a couple of passes. . .30 seconds at most with a nice clean stone.

Here is the type of stone that you sill probably want to use so that you can get into the small areas in these cutters. . .this is a rectangle stone 1/2" wide and 1/8" thick, very fragile, but easy to get into tight spaces.

http://www1.mscdirect.com/cgi/NNSRIT...-SearchResults

a half round one like the link below is nice as well, this one is 3/8" diameter so it should be large enough to hold on to, but small enough to allow enough clearance.

http://www1.mscdirect.com/cgi/NNSRIT...-SearchResults

As far as the spiral flutes go. . .theoretically they should make the drill cut smoother, in other applications (such as reamers) this is very true, especially for interrupted cuts, but I'm not sure how much difference it would make with a step drill. . .probably more dependent on the thickness of stock you are drilling than anything else.

I hope this helps.

[mebuildit]

These work great for making true to size holes. I use these a lot in my mill or drill press.