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I pretty regularly use a carbide spot drill to pre-drill holes to then open out with an end mill running a bore or adaptive toolpath in Aluminium, I started doing that after killing a couple of endmills in the initial helical ramping.

With this thickess of material, the chip being as tightly spiraled as it is, and it being aluminum, I’m not too worried about chip wrapping. Also, it’s on a pretty clear expanse of flat plate. If you’re drilling down inside a pocket or close to a step or a clamp, you can get the “weed-whacker” effect where the chip hits something and bounces back toward the tool. If it doesn’t break, it could potentially wrap.

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Cutting speed forstainless Steelwith carbide

Can you let us know what machine you’re using and what grade of metal it is? The hole looks clean but I can’t help feeling that the spiral chip would get really tangled up if drilling a lot of holes.

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IMO 0.001 feed per rev is pushing the minimum I would go, that’s 0.0005" chipload and starts to get iffy on the chips ability to carry the cut’s heat with it. A thicker chip will be better for heat management and should help break them which can be easier on the tool. Ive found that 0.002-0.004" FPR is the magical sweet spot for carbide drills (depending on helix). Might require an HDZ or other ballscrew Z axis to push them with enough force though.

High Speed Machining (HSM) What is High Speed Machining (HSM)? High speed machining (HSM)--also called trochoidal milling, adaptive clearing,

Instead of retracting a drill, you could go right into milling with the same tool in the same hole with it already at full depth.

The rake angles should be between 3 and 8 degrees, larger angles suiting austenitic stainless steel grades (304, 1.4301 316, 1.4401 etc). Margin widths should be 0.125-0.35 mm for HSS tools and 0.05-0.125 mm for carbide tools. The margin width should increase, within these ranges for larger tool diameters. The preferred tool angles (degrees) are summarised as follows:

Stainless steel speeds and feedscalculator

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Also, this video spurred me to learn something new - that the term quadriplegic includes people affected with partial paralysis of the limbs. I had always associated the term with complete paralysis previously.

The work hardening effect when drilling the austenitic stainless steel grades eg 304 (1.4301), 316 (1.4401) is the main cause of problems. The steel hardens progressively as it is cold worked, but it also important to make sure that the steel is fully annealed (softened) when deep or small diameter holes are to be drilled. Cold drawn bar products should be avoided. As with any machining operation, rigid machines and tooling should be used when drilling or reaming. Drilling jigs should be used, where possible, to help keep the work-piece rigid.

Stainless steel speeds and feedspdf

“The threshold for aluminum is something like 60,000 sfm, which is enormously fast,” he said. “I’ve seen aluminum run at 24,000 sfm with an uncoated carbide insert, and it didn’t harm the aluminum or the insert. I tell our customers that, within a safe working environment, don’t be afraid to crank it up because I’ve seen that higher speeds in aluminum gets you both better tool life and a better surface finish.”

Normally the web thickness increases along the length of the drill (away from the point). When the drill tip is being reground, the exposed web should also be thinned to compensate for grinding back up the length of the drill.

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During drilling it is essential to maintain the feed to cut through the work hardened layer generated as the metal is cut. Dwell or rubbing must be avoided. Entry and re-entry after backing out should be done at full speed and feed rate.

He has been hand machining and drilling 1000’s of holes to make adaptive reachers for quadriplegics every year for the past 20 years on an old bridgeport knee mill so I’m excited to help my friend to get into doing Cnc work for the first time. His tools changed my life and I couldn’t live independently without them so to help him help others is a pleasure and the least I can do.

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Cold working during drilling, punching or machining the preparation hole prior to reaming austenitic stainless steels must be minimised. Sufficient material must be left on the hole wall however to allow a positive reaming cut to be made to undercut the new work-hardened layer produced.

For normal clockwise tool rotation, right hand spiral tools cut more freely than left hand spiral tools, but tend to self-feed into the hole. Left hand (reverse) spiral tools have a lower tendency to self-feed which can be beneficial when precise feed rate control is needed.

I like the video. I wonder if some of the setups where the mill head is angled over could be avoided with fixturing that holds the workpiece at an angle (or one of those tilt-type tooling vises).

Those ones you show look like they have a decently high helix angle, which was also recommended in the above link. I’d say give 'em a try if the price is reasonable. I don’t think the tip angle is going to be super-critical. 118 is the common angle for jobber drills that have been used for years and years.

Although standard High Speed Steel (HSS) drills are suitable for drilling stainless steel, they should preferably be shorter to reduce deflection and breakages in use. Carbide tipped drills can also be used. The web thickness should be around 1/8th of the drill diameter, except for small diameters where thicker webs improve the strength and rigidity of the drill shank. This can however impede chip flow. Conversely, with a thinner the web although the drill will have less rigidity, chip flow and removal should be easier and it is easier to get the drill to start the hole.

I’ve also used regular ‘jobber’ drills in the spindle for repetitive drilling ops where I didn’t want to wear out nice carbide tooling and that works well too, at well under $1 per drill bit you just replace them as they blunt.

I like the idea of drilling out the center of the 3/8" holes with the 1/8" bit and then milling out to full size. I’m assuming the latter would be done at full depth to spread wear along the length of the cutter.

Thanks for posting this I am looking into drilling on a cnc router for a friend that needs to drill hundreds of holes in 3/16 aluminum bar stock.

I went with 10,000 rpm for a surface speed of 233 SFM and feed rate of 10 IPM for 0.001" per rev. Put a little drop of 3-in-1 oil on the plate and a little on the bit and voila!

Excessive feed pressure, poor cutting with sharp drills or drill breakages can indicate that the drill tip has an insufficient lip relief angle. Conversely, if the drill is tending to dig-in then a reduced lip angle may be better. In any event, it is essential that drills are sharp and properly ground.

When drilling through-holes a backing plate should be used to help avoid drill breakages as the drill comes out of the blind side of the hole.

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Those Kyocera PCBs I have are 130 degree. I think the angle is slightly different when they get over a certain size ( I think I saw that in the ebay listing description for them).

150-400 SFM is the recommended surface speed for drilling aluminum with carbide and this calculator recommended 0.0008 to 0.0018" per rev for the feed.

Spiral fluted reamers are preferable for working with stainless steels as they produce less chatter and help the flow of chips better than straight fluted tools.

To avoid tool changes and having to revisit the same holes, the 3/8" holes could be done with a combo drill / end mill. I would think the style with the twist-drill type point would be best (what they call “Drill Style - 2 Flute” here):

In the Shapeoko, with a spindle capable of running well at low RPM the limit seems to be how hard the Z axis can push down to meet the feed per revolution required to be cutting instead of rubbing. I’m up to about 4,000RPM on the 4mm bits now. At a certain point increasing the RPM and Z feed rate the whole X gantry starts to vibrate and I chicken out and back off. In Aluminium I add small amounts of Isopropanol as lubricant as that’s largely ‘self cleaning’ as it evaporates away.

SFM forstainless steeldrilling

Millingspeeds and feedsChart

Tested on scrap 1/8" plate, drilled all in one go. I read up on peck drilling and that wasn’t recommended unless you’re going deeper than 3x the diameter of the bit. This page seemed to have some good recommendations on peck depths:

I was using a clearance plane of Z 0.125" and went down to Z -0.166" (0.125 material + 0.021" drill point + another 0.020" to make sure it went all the way through). 0.291" total travel at 10 IPM is about 1.75 seconds. Rapiding back up out the same distance at 100 IPM would be about 0.175 seconds. Total cycle time of about 1.93 seconds.

Traditionally high speed steel (HSS) tools have been used for drilling and reaming, but carbide tipped tools are also used for specialised jobs or long production runs. This article gives suggested feeds and speeds for drilling and reaming taken from the BSSA Stainless Steel Specialist Course Training Note No9 ‘Machining Stainless Steels’.

304stainless steelcutting speed

Centre punching with conventional conical shaped punches can result in enough localized work hardening to make drill entry difficult. This can make the drill tip deflect or wander, glaze the surface and/or blunt the drill tip and result in drill breakages, particularly where small diameter holes are being drilled. Where a punch mark is needed to help get the hole started, a light mark using a three-cornered pyramid tip punch is a better idea.

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True - this is definitely a thin chip at 0.0005". I’m fairly confident that I could double the feedrate without issue. I will have to try that next time I fire up the machine.

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I’ve found that both chip extraction and some small amount of lubricant / coolant are key to using the carbide drills and not getting a hot workpiece, I’m not up to the SFM where the temperatures start to drop back down and I’m not sure this machine can get there.

Turningspeeds and feedscalculator

Stainless steel speeds and feedschart

Yes it will ramp down to full depth then open it up. I figured pre drilling will help take the plunging load off the endmills work and speed up the cycle time. The work will be done on a Tormach 24r which is a linear rail ball screw machine that should be fairly rigid. Had the HDM foot print been large enough I would of had him go that route but he needs 40" of travel for his parts.

Finally got around to trying this out. 0.089" (2.25 mm) is the tap drill size for a 4-40 thread. Carbide circuit board drills are typically 1/8" shank and come in a range of sizes, including sizes larger than 1/8":

It may be necessary to reduce tool speed to ensure that the feed rate can be maintained, without causing other problems. Drilling chips must be allowed to get away from the hole being drilled, freely. Any build up of chips in the hole can cause roughness of the hole-wall, or in cases of severe clogging, drill breakage. When deep holes are being drilled, the drill should be backed-out frequently with minimum dwell as follows:

I’m hoping he can reliably run an 1/8" stub drill with air blast and light lubricant mist. He needs 1/8" and 3/8" holes. My thinking is drill everything with the 1/8" drill then use a 3mm Datron single flute stub mill to go from 1/8’ to 3/8" where needed.

To improve the surface finish of the finally reamed hole, the speeds suggested can be reduced by 50%. Rough finished machined surfaces or dulling or burning of the cutting edges usually indicate that the speed is too high.

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Both too slow and too fast drill speeds can cause drill breakages. It is important that small diameter drills are not used at too slow a speed. Excessive speed however is a major cause of drill breakages. Drilling machines with continuous speed change control are better than stepped or discrete speed change gear boxes for drilling stainless steel. When drilling deep holes, reduce the speed and feed as the drill moves into the metal. With depths up to 3 times the hole diameter, no reduction is necessary, but with deeper holes, the speed and feed should be reduced as follows:

The holes will be drilled prior to bending with only 2 holes being drilled in a angle jig. I had him try it flat but those hinge holes deformed when bent so they have to be done after the bend.

I looked into them as the first option but I don’t know long the sharp point will last with non stop drilling. From my understanding they are for light drilling not for constant drilling as the point quickly wears out. I couldn’t find any drill mills with 118 degree tips.

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Yes, the mill/drills could be one of those situations where you compromise some of the attributes of each of the two tools by combining them into one. This page recommends 130 to 140 degree angles for aluminum:

The cutting angle should be around 135 degrees. Larger angles produce thinner chips that should be easier to remove, which is important when drilling stainless steels. Lower angles of around 120 can however be used for drilling free-machining grades (eg 303 1.4305). Wear to the drill point can indicate that a larger point angle should be used. Both cutting edges must be at the same angle to the centre line of the drill and be the same length. A mixture of chip sizes can indicate that that the two cutting edge angles and lengths are not the same. Lip relief angles decrease as the drill diameter increases and suggested angles are: 3mm – 16 degrees 6mm – 14 degrees 12mm – 12 degrees 20mm – 10 degrees 25mm – 8 degrees