Blowout on Walnut

[Wichman]

I am working on the double lidded work basket pattern from the Classic Fretwork Patterns book. I am cutting a stack of three 5/16" boards, 1 oak and 2 walnut. I am using a #65 drill bit, cobalt alloy, in a drill press, 3500 rpm, against a fresh wood backer. And I'm still getting a lot of blowout on the bottom walnut piece and I have broken three drill bits in the process (these drill bits generally last for more than a year apiece. The drill bits were also bending during the drilling so that I couldn't depend on the exit hole being inside the waste area in the pattern. So far it's not a total disaster, but the bottom layer will not be a premium piece.

Any suggestions as to what is going on and tips or tricks going forward?

 

 

[Peter N White]

You are drilling nearly 1 inch and you need to drill very short depths back  out and clear swarf. Will be fairly slow going.

[kmmcrafts]

Sounds like you're drilling in too fast for the drill bit.. Possibly a bad batch of drill bits? I like the Mascott drill bits from Denny..  But when you say the bits are bending and not going straight makes me think you're pressing through too hard. 

A good way to see if you're drilling too fast for the bit is.. look at the chips coming off the bit.. No chips pile up around the bit as you're drilling and when you pull back up a large twisted chip clears out of the chip groove.. you're going too fast for the chips to clear out.. should be a fine pile of sawdust chips.. Drill down a short 1/8 - 1/4 raise back up to clear chips and then go back for a little more.. will help you from going too fast. 

[Scrappile]

Those tiny bits can dull real quickly.  have to go real slow with your downward pressure. 

[tomsteve]

if the bits are bending theres too much pressure on them. gotta let them do their work. the blowout on the back- with a backer- indicates either too much pressure when drilling or the workpiece isnt tight against the backer.

i like to drill 1/4" or so , back out so the chips and clean out of the flutes, drill more.

its possible,too, that the drill bits dont have the right grind on the cutting edge

 

when possible i put entrance holes in the center of a cut- blowout being one of the reason. also because i can also apply too much pressure when drilling and have the hole end up a little "off". ive drilled thousands of holes and can still try to go too fast when drilling. 

maybe ill "get it" in another 3,926 holes drilled. :)

[Wichman]

You do realize that I posted this advise to the board about two weeks ago, right?

This pattern has 315 pierced cuts, so about 325 holes ( extra holes for cutting around the outside of the pieces ), These current projects will make 6 total; so 1300 holes, just on this pattern. This ain't my first rodeo.

When I can see the deflection of the drill bit before it actually starts to cut the hole, I will shift the blank to the soft spot and try again. Sometimes this works sometimes not. I've started to use clip on magnifiers ( 3x ) while drilling and while threading those small blades. For drilling I can easily see when the blade deflects when starting the hole.

I'm retired so I don't have to push for time, slow and easy is the name of the game. Even before I retired I would leave a half-dozen cuts or so from finishing a piece and come back to it the next day, well rested. With several hrs of cutting in a piece I don't want to rush and ruin it, and waste the time already invested.

I would switch to a larger drill bit, but I'm at the limit now for some of the holes. I've thought of using an awl to make a start point but that won't help the bending in the middle.

I bought the Hegner so I could stack cut and be more efficient with my time, so it's somewhat annoying that the drill bits are being the limiting factor in how many I can stack.

 

 

[kmmcrafts]

Hard to see in the photo for sure but it also looks like the boards are warped / cupped.. That can affect how the drill goes through the stack as well.. ( especially on cheap or dull bits ) When I have a slightly cupped board I will sometimes use a awl to make little indentations so the bit has more of a direction to follow.. IF it's cupped some these tiny bits do track off of where it intended to start and then it starts off crooked.. then the bits are small and a little flimsy, they will bend because they start off crooked and track the rest of the way crooked.. Chucked in the spindle in one spot and drilling off that center makes the bit bend..