Drill sharpening: What am I doing wrong?

[Petromax]

I tried to grind several drills. The result seems to be okay, but after drilling just one hole in mildsteel, the point of the drill is getting blue. My conclusion is that the drill is overheated at the very top of the drill. The cutting performance is not very bad, but I expected more.

What am I doing wrong?

(HSS drills 8..10mm, 118° top angle, 11° cutting angle)

https://www.dropbox.com/s/q63r507ob287x51/20151227_141004.jpg?dl=0
https://www.dropbox.com/s/41g87wfkezm6ktr/20151227_141122.jpg?dl=0
https://www.dropbox.com/s/y0ld6ohofocj9dl/20151227_141424.jpg?dl=0

I took this picture after drilling one hole.

https://www.dropbox.com/s/w4i98xklp3jha2k/20151227_142217.jpg?dl=0

[Ken S]

Welcome to the forum, Paul.

I am no machinist, however, you don't mention whether or not you are using oil to help cool the bit. Hopefully someone like Elden who worked in a machine shop will answer.

No matter how a bit is sharpened, speed, feed and lubricant matter.

I don't mean to be critical, just trying to rule out some of the obvious gremlins.

Ken

[Jan]

Paul, you have burned the drill bit. Ken advises you well. 

The standard way of drilling a hole larger than some 8 mm is following:

a)   Use a punch to make a depression in the metal.
b)   Use a two bit process. The pilot hole is usually half of the final diameter you need.
c)   Use cutting oil, which lubricates and cools the drill bit and also helps to remove chips. Lubricate often. Add lubricant whenever the previous drop evaporated. Drop lubricant on both sides of the spiral in the drill bit, it will dramatically improve the life your drill bit.
d)   Reduce the spindle speed and feed rate when drilling larger hole.

Jan

[Elden]

   Welcome to the forum, Paul. Here is a link to a simple and basic speed chart for bits. I don't believe it takes different kinds or hardness of steel in account.

http://www.woodmagazine.com/woodworking-tips/techniques/drilling-boring/drill-press-speed-chart/

   From personal experience, steel can become work hardened while drilling a hole. That is one thing that will lead to a burnt  bit and a battered drill bit.

   An excellent source of metal working lore is found in the YouTube videos produced by tubalcain (mrpete222). He has some on drill bits. A playlist of 200 of his videos can be found at the following links.

https://m.youtube.com/#/playlist?list=PLBC69869E8CB708F2
https://m.youtube.com/#/playlist?list=PL6HIFled82YXCXpWVcoMvHxr7_qQsXkzR

   tubalcain drill bit videos 1-3 can be found by clicking on the following links:

https://m.youtube.com/#/watch?v=hJItj_ISurY
https://m.youtube.com/#/watch?v=rUMTJ9GZIC8
https://m.youtube.com/#/watch?v=cqn2VPGYA9c

[Petromax]

Thank you for your replies. Yes I reduced the speed, but used no cutting oil. I also thought there was no need to pre-drill with a smaller diameter when I use a four facet drill.  Maybe there is something wrong with the geometry.


I'll try again...

[Herman Trivilino]

Thank you for your replies. Yes I reduced the speed, but used no cutting oil. I also thought there was no need to pre-drill with a smaller diameter when I use a four facet drill.  Maybe there is something wrong with the geometry.

I don't know much about it, but I have seen steel workers on construction sites routinely drill half-inch diameter holes in soft steel with no pilot hole or lubricant. They used a drill press with a low rotation speed.

I believe the key thing is to avoid over-heating. All of the tips you received seem to be precautions against that very thing happening, so hedging your bets is the safe way to go.

Reminds me of an old lawyer's joke.

"Your Honor, I will show first, that my client never borrowed the Ming vase from the plaintiff; second, that he returned the vase in perfect condition; and third, that the crack was already present when he borrowed it."

[Ken S]

Good post, Herman. It gave me a chuckle!

I think we should differentiate between practice and good practice. As a working telephone man, I subjected my poor drill bits and drills to many expediencies. It got the job done, however, I would not dignify these experiences as "good practice". Alas, drill bits are often abused.

Ken

[Jan]

I don't know much about it, but I have seen steel workers on construction sites routinely drill half-inch diameter holes in soft steel with no pilot hole or lubricant. They used a drill press with a low rotation speed.

I believe the key thing is to avoid over-heating. All of the tips you received seem to be precautions against that very thing happening, so hedging your bets is the safe way to go.

Herman, you have written a good comment. Recently many machine shops and plants are experimenting with machining dry. 

The main reason is economical, because maintaining the cutting fluid regime is an expensive task. So, the manufacturers are ready to accept shorter tool life, when it is compensated by lower total cost of the machining project.

Very important, from the technological point of view, is creation of good chips, because they can carry away most of the generated heat.

For example, carbon steel and alloyed steel does not require cutting fluid, while low-carbon steel becomes adhesive during drilling and the cutting fluid works mainly as lubricant preventing welding. This could be the cause of Paul's problems with freshly sharpened drill.

Nevertheless for some materials dry machining is difficult or seldom option (stainless steels, powdered metals, nickel-chromium alloys, titanium).

Jan

[Petromax]

I'm still having problems whith sharpening my drills. Here are some pictures from the steps I took:

1. Mounting the drill:
https://www.dropbox.com/s/zw8c6gllflffb8t/Screenshots_2016-01-08-16-30-45.png?dl=0
https://www.dropbox.com/s/lwx8wv584aiv9o6/Screenshots_2016-01-08-16-28-18.png?dl=0

2. Setting the point angle at 118° and the clearance angle at 11°
https://www.dropbox.com/s/rynqvs5pp05nd1o/Screenshots_2016-01-08-16-31-28.png?dl=0
https://www.dropbox.com/s/qyolpq35jb97ocu/Screenshots_2016-01-08-16-29-38.png?dl=0

I just focus on the primary facets. After grinding, the drill is still correct aligned. The I checked the point angle and as expected,  the angle is 118°.
https://www.dropbox.com/s/tfa1pnkpzkl2hv0/Screenshots_2016-01-08-16-32-43.png?dl=0

But when I check the clearance angle, I noticed there is something wrong. The angle is negative, so point (A) is rubbing the surface and the drill generates heat. Drilling a hole in wood is not a problem, but (mild)steel is not possible without overheating the drill.
https://www.dropbox.com/s/qep7ik0o1xd0pv2/Screenshots_2016-01-08-16-42-45.png?dl=0

I took also a picture from an other (new) drill. As you can see the is a neat clearance angle.
https://www.dropbox.com/s/zun9a05y4yv88fo/Screenshots_2016-01-08-16-34-29.png?dl=0

What am I doing wrong?

[Ken S]

Petromax,

I am out of practice with my DBS-22. In your dropbox photos I did not notice you setting the distance from the universal support and the grinding wheel. Also, I did not notice you grinding the secondary bevel.

Whenever I sharpen a drill bit, I first watch Alan Holtham's video. If ou can pause the video between steps, it may simplify things for you. Once you get the jig working correctly, the results are worth the frustration.

You should not have a negative clearance angle.

Hang in there. This will work. Keep posting.

Ken

[Johan_E]

How big is the gap between the universal support and the grinding wheel ? Your Dropbox pictures do not show it. The base plate looks too flat mounted.
It looks like it is much more steeply mounted in this video.
https://youtu.be/KqcMTxrIoPY

[Petromax]

Petromax,

I am out of practice with my DBS-22. In your dropbox photos I did not notice you setting the distance from the universal support and the grinding wheel. Also, I did not notice you grinding the secondary bevel.

Whenever I sharpen a drill bit, I first watch Alan Holtham's video. If ou can pause the video between steps, it may simplify things for you. Once you get the jig working correctly, the results are worth the frustration.

You should not have a negative clearance angle.

Hang in there. This will work. Keep posting.

Ken

Hello Ken,

I used the setting template for the distance and the angle:
https://www.dropbox.com/s/5k8r28y10wt40se/20160108_152810.jpg?dl=0


Indeed, I did not grind the secondary facet, just to show that the clearance angle of the primary facet is not good and this is the reason why the tip of the drill is getting to hot.

https://www.dropbox.com/s/xrfvhvx77zb7ojx/blue%20tip.jpg?dl=0

[Elden]

Paul,

    Like Ken, I have not used the DVD-22 for quite a while. I have not used it a lot but some. I have sharpened a fair amount of bits through the years free handed using a bench grinder. Looking at the following picture, it appears to me that you do have small amount of relief right behind the cutting lip.

https://www.dropbox.com/s/qep7ik0o1xd0pv2/Screenshots_2016-01-08-16-42-45.png?dl=0

   If I was grinding by hand, I would grind the relief by rocking the bit down, as Tubalcain explains, starting at about the 8 minute 50 second point in this video.

https://m.youtube.com/#/watch?v=cqn2VPGYA9c

   His method is the same I was taught years ago, except we used a grinder.

   I think, possibly, the bit you have pictured would cut if the relief were to be ground in, without touching the cutting lip. Grinding the secondary facet on the DBS-22 should accomplish it as well. I do not remember how my bits looked after the primary grinds before doing the secondary grinds using the DBS-22.

   I still use hand grinding. Last year, I picked up a flat of approximately 100 drill bits at an auction. They were all dull and some were extremely abused. 2 or 3 had to have 3/8 to 1/2 inch (9.5 to 12.7 mm) of the length removed to restore the cutting surfaces. A bench grinder with a coolant dipping pan definitely has its place in the sharpening shop. They have been free handed, some may eventually meet the DBS-22.

[Johan_E]

Do you use the hole in the template to set the distance between the universal support and the grinding wheel ? Watch this video. It will start at the 50s when he shows how he sets the distance.

https://youtu.be/KqcMTxrIoPY?t=50s

/Johan

[Petromax]

Thank all of you for your help. In my opinion, the DBS-22 gives a lot of hassle. Maybe my expectations were to high. After seeing Tubalcain video, I regret I haven't bought a belt grinder for €180 instead of a DBS-22.