sharpening to ream an existing hole

[Ken S]

I overlooked the broken drill instructions in the DVS-22 instructions. (Rich found it)

What piqued my interest was on page 15: (Sorry, I am not having luck copy pasting the page here.) Under the subject of reaming an existing hole, it states that grinding the secondary bevel is not necessary. For a metal worker or a very careful woodworker beginning with a center drill and then enlarging the hole, this could save much sharpening time. For online Fine Woodworking subscribers, Ernie Conover did a fine video on very accurate sizing of drilled holes in wood.

For a professional sharpener, adding the secondary bevel has a wow factor, which the customer may expect. However, for one's own shop use perhaps only the primary facets are necessary on many larger bits.

Ken
 

[Elden]

 From page 15 of the DBS-22 manual:

"Reaming an Existing Hole If you need to make an existing hole larger, you do not need to grind the secondary facets. However the existing hole  ∅  D  must be larger than the chisel edge,  C."

   I couldn't get their image to show, either. This picture shows what the chisel edge is. They are saying the diameter of the existing hole needs to be larger than the chisel edge.

   I come from a farm background. We have drilled many holes using only a center punch to make an indentation in the metal to start the chisel point drill bits in. Grant it, we were not talking 0.003 inch (0.076 mm) tolerances! 

[Jan]

For your convenience I am attaching the drawing from the page 15. 

Jan

[Jan]

I do not have the DBS-22 attachment and so I use my homemade jig for drill bit sharpening (https://forum.tormek.com/index.php?topic=3226.0)

My drill bit sharpening session is organised in the following streamlined way:

1)   I grind 10° lip clearance for primary facets of all drill bits,
2)   I grind 20° clearance angle for secondary facets of all drill bits,
3)   I hone the cutting lips.

This batch method is not applicable for the DBS-22 attachment where each drill bit has to be carefully mounted into the drill bit holder and then both facets sharpened.

Jan

P.S.: Recently I have been thinking about sharpening the leading edge of the drill body land's. I have not tested it yet but do not expect principal difficulties. 

[Jan]

In the attached picture you can see my simple approach to sharpening the leading edge of the land's. I have just replicated the existing edge clearance angle (circa 10^o). 

Drills with regular or slow spiral allow for better alignment to the wheel's face.   

Jan

P.S.: Elden kindly reminded me, that the land lips sharpening will reduce the diameter of the drill bit. So please be aware that you can reduce the bit diameter by 0.1 mm (0.004") or more!

[RichColvin]

Multiple facets are important, even when widening an existing hole, & especially with metal. 

There is a very good article on this at :  http://www.newmantools.com/machines/drillpoint.html

An excerpt on facets is : 

Multi-faceted geometry generates the least amount of heat of all the drill point patterns. In comparing two drills of the same diameter, the multi-faceted drill features 150% less thrust and 70% less heat than a conventional drill.

In fact, some older machinists added a tertiary facet for even more relief. 

I wouldn't skip the step of adding the secondary facet.

Kind regards,
Rich

[Elden]

Rich,
   Thanks for posting the interesting article.
_________________________________

For the cool pocket change amount starting at approximately $2100 USD, you can own a machine capable of the grinds listed in the article!
   

[Ken S]

Rich,

Thanks for posting a very interesting article. I have downloaded and printed it. Not being a machinist, this more sophisticated multipoint sharpening will take a while to sink in. Until the DBS-22, it was not even possible for me.

I still like Leonard Lee's wise advice about drill sharpening in his book: Start with high quality USA made drill bits.

Ken

[RichColvin]

Ken,

I don't know if there are any US-made drill bits any more. 

The best new ones I have are German-made cobalt bits (got them in Singapore to have a good set of metric ones).  Really, really good !

And, as any machinist will tell you (even the amateur ones like me), you need at least 4 types :  metric, imperial, numbered, & lettered.  Oh yeah, and for woodworking, you also need Forstner bits :  but that's a whole different sharpening approach.

Kind regards,
Rich

[Ken S]

Rich,

Alas, US made drill bits are becoming rare. They are not extinct yet. Among other companies, Ohio Drill and Tool is still making drill bits in Homeworth, Ohio.

You are quite correct about the four types of drill bits. I picked up good, slightly used US made sets of all but the metric bits. (No slight meant to metric; I just have not gotten around to it. I certainly wish I had them when I fitted the Norton 3X wheels to the 12mm Tormek shaft. 31/64" and reamed is not a good method.)

A skilled craftsman is a skilled craftsman, regardless of location. Unfortunately, companies exploiting cheap labor also exploit the customer with inferior steel. Well maintained quality drill bits should last a very long time and cost less in the long run. A set of quality drill bits regularly sharpened with the DBS-22 four facet profile should be listed as part of one's estate.

Ken

ps Rich, you have convinced me that ignoring the secondary facet is unwise.