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8mpg

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#1
Im building a 2x72 grinder and it uses 1.5" solid steel bar for the arm. I have drilled one of two holes. The second hole just wont drill. At first I thought it was the cheapo Harbor Freight drill bit set (though they have acutally worked great) so I sharpened the couple bits. After sharpening...it still wont drill. Any ideas? Im using cobalt HSS bits. Did a 1/4" pilot, stuck on a 3/8" opening and need to open it up to 1/2".
 

mikey

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#2
Are you using a drill press or hand drill? What kind of steel? When you re-sharpened the drill, did you put enough relief behind the cutting edge?

Assuming your drill is sharp, I would slow the speed down and increase feed pressure. You may have some work hardening and this should help you punch through it. There are all sorts of things you can try - end mills to cut through the hard stuff, carbide drills, etc.

If I had to guess, I would suspect your drill's geometry.
 

8mpg

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#3
I have been using the mill to cut the steel. Its 1018 cold rolled I believe. I was worried about work hardening but am new to this so I wasnt sure. The drill has been sharpened in a drill doctor and looks good. I can add some clearance though by hand. I'll try an end mill.

What kind of RPM would you suggest? I have been doing about 800rpm on the mill.
 

ttabbal

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#4
RPM seems pretty close for a 1/2" bit. If you managed to harden it though, perhaps ~500 RPM and more pressure? Do you have a carbide end mill you can use to remove some of the material? That might work better on work hardened 1018. It could just be a thin skin you need to break through, think mill scale on hot rolled steel. You could also try another piece of similar material, perhaps a bit of scrap sheet, to verify your sharpened drill geometry.

Just a small point, a grinder arm doesn't need to be solid. Tube will be plenty strong, and it's a lot easier to drill. :)
 

BaronJ

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#5
Hi 8mpg,

800 rpm is a bit fast for a 1/2" inch drill in 1018. 450 rpm would be nearer the mark.
 

4ssss

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#6
At first I thought it was the cheapo Harbor Freight drill bit set[/QUOTE]

That says it all
 

jakes_66

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#7
I've been frustrated by cheapo drill bits... It'll make you a believer in quality HSS in no time flat.

Can you post a closeup photo of the end of your drill bit? It would help diagnose the issue.
 

benmychree

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#8
I have not seen 1018 to work harden, it does not have enough carbon content to harden appreciably, although, sometimes if you are running too fast, and the drill goes (very) dull, a bit of HSS can be wiped onto and bond with the CRS, usually running slow with plenty of feed pressure can bite through the hard layer, or as suggested a carbide end mill can do the job. In my opinion, cheapo drill bits are not worth owning. Another point is that when drilling pilot holes, they should not be bigger than the thickness of the web of the finish size drill, and stepping out such a small hole as 1/2" is not advisable, due to the tendency to wobble, and/or hog into the previously drilled hole, possibly breaking the drill or yourself and damaging the equipment.
 

JimDawson

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#9
Sounds like you need to slow down the drill bit and use more pressure. 1018 will locally work harden when drilling, especially if you are using coolant as a cutting fluid, but normally a bit more pressure will break through the surface hardness. 1/4 inch is more than enough pilot hole for a 1/2 bit. The Harbor Freight cobalt bits are normally quite good, I have several sets.
 

8mpg

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#10
Thanks guys for the advice. I was able to get through it with an end mill which is HSS. I'll slow down more when I drill. I have a slight problem as the mill uses a VFD and it seems like low RPM it loses some power.

The drill bits... I bought them because they were recommended here. They have done great until now which is probably my fault for going too fast. If I recall, when I started drilling, I was in the 1100rpm range because I wasnt paying attention. Once I noticed I slowed down. Good to learn about the pilot hole size and the web size on the larger bit. Makes sense and something I didnt know. Since I bought the bits, I'll continue to use them and sharpen them.

There are many many more tools I wish I had (reamers, lathe, better end mills, etc). Over time I'll slowly grow my collection. I just need to find some quality stuff that doesnt cost and arm and a leg.

Thanks again for the advice everyone!
 

ttabbal

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#11
Gotta start somewhere, like all of us. :)

I have some HF stuff I keep mostly so I can heat and beat it into weird shapes when I get a forge running. I think it will make me feel better, and I get some artwork. The cobalt drill bits are supposed to be ok, for HF anyway, but I haven't used them.

Does the mill have a back gear or pulleys? On mine, I set the pulleys/gear to get close, then VFD to fine adjust. Every machine is different though.
 

P. Waller

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#12
I do this all day long in different materials, for a living.
For a 1/2" HSS twist drill in 1018/A36 steel I would begin at 50 FPM cut speed, around 375 RPM's and NO LESS then .004" per revolution feed rate, if using water soluble flood coolant, if using flood cutting oil start faster.

Do not pilot drill, spot the hole and drill to size in one shot. HSS twist drills are the least expensive tooling that you will ever buy, if one lasts 50 parts buy 5 if 200 parts are needed.

Do not baby the feed rate as mentioned above, force the tool to cut at all times, if a through hole most of the damage will occur when it passes through the far side of the hole, this is mostly unavoidable but there are strategies to make this less of an issue.

This is a 1 5/16" twist drill through 3" of 1018 round stock, no spot, no pilot hole, straight through with no pecks.
If you listen to the audio the sound of the drill passing through the far side is obvious, this causes the drill bit all manner of problems.

32 parts drilled at less then 4 minutes each using 1 used unsharpened drill bit.
180 RPM's (62 FPM) and a .008 per revolution feed rate. If I had 320 parts I would have used a carbide insert spade drill.

 

8mpg

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#13
Great info. I had always learned the "let the tool do the work" and not to use too much pressure. Seems like its the opposite in these cases.
 

rwm

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#14
I have a Drill Doctor...not impressed. Hard to get the geometry right with a device made from flexible plastic.
Robert
 

P. Waller

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#15
Great info. I had always learned the "let the tool do the work" and not to use too much pressure. Seems like its the opposite in these cases.
If you baby the feed you will simply rub the tool on the work, doing so will over heat it and cause rapid tool failure, the tool must cut at all times.
When a twist drill passes through the far side the chip becomes very thin because there is no material left, the dimple produced will often turn blue from the heat unless there is excellent coolant flow at the bottom of the hole. Coolant through drills help with this.

Drilling through holes in certain stainless alloys will make this abundantly clear.
 

P. Waller

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#16
Also do not spin a drill to fast for the drill material.
 

8mpg

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#17
Thanks again for the advice! I have a lot to learn
 

plunger

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#18
I do this all day long in different materials, for a living.
For a 1/2" HSS twist drill in 1018/A36 steel I would begin at 50 FPM cut speed, around 375 RPM's and NO LESS then .004" per revolution feed rate, if using water soluble flood coolant, if using flood cutting oil start faster.

Do not pilot drill, spot the hole and drill to size in one shot. HSS twist drills are the least expensive tooling that you will ever buy, if one lasts 50 parts buy 5 if 200 parts are needed.

Do not baby the feed rate as mentioned above, force the tool to cut at all times, if a through hole most of the damage will occur when it passes through the far side of the hole, this is mostly unavoidable but there are strategies to make this less of an issue.

This is a 1 5/16" twist drill through 3" of 1018 round stock, no spot, no pilot hole, straight through with no pecks.
If you listen to the audio the sound of the drill passing through the far side is obvious, this causes the drill bit all manner of problems.

32 parts drilled at less then 4 minutes each using 1 used unsharpened drill bit.
180 RPM's (62 FPM) and a .008 per revolution feed rate. If I had 320 parts I would have used a carbide insert spade drill.

I dont think this would work on a garden variety 13x40 chinese lathe. :)I think the tailstock nut would strip.Nothing nicer than some serious rigidity in a machine.What capstan is that .? Looks like a russian tank
 

vocatexas

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#19
I believe that's a Warner and Swasey lathe, possibly a Number 3.
 

P. Waller

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I dont think this would work on a garden variety 13x40 chinese lathe. :)I think the tailstock nut would strip.Nothing nicer than some serious rigidity in a machine.What capstan is that .? Looks like a russian tank
Warner & Swasey #5 turret lathe of 1950's vintage, a very powerful machine.
This is my version of humor, I realize that most hobby machines will not do this but the principles remain the same.
 

BaronJ

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#21
Hi Guys,

I've seen similar ! A Ward No:3 pushing a 65 mm hole through a 75 mm thick cast iron pulley in one go, prior to fitting a taper lock bush.
Awesome !
 
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