Straightening a valuable drill bit

[Norppu]

Years ago, I bought a 16mm parabolic drill bit from a flea market in Frankfurt. Such drill bits are quite valuable. The price of this particular drill bit when new is 200 euros.
At the flea market, the price of the drill bit was 20 euros, which I thought was a good deal.
Unfortunately, I noticed that the drill bit was badly bent and in its current state completely unusable.
Could it be straightened?

This video features:
- Solberga (1975) Column drilling machine

The video is here

 

[projectnut]

Years ago, I bought a 16mm parabolic drill bit from a flea market in Frankfurt. Such drill bits are quite valuable. The price of this particular drill bit when new is 200 euros.
At the flea market, the price of the drill bit was 20 euros, which I thought was a good deal.
Unfortunately, I noticed that the drill bit was badly bent and in its current state completely unusable.
Could it be straightened?

This video features:
- Solberga (1975) Column drilling machine

The video is here

The price of 200 euros is a bit stiff even today for a 16mm parabolic drill. There are currently several listings on eBay with prices in the $20.00 range. Some even have "best offer" which means they will take even less. McMaster (which is usually more expensive than most vendors) has them for $56.00 a copy. For that price I wouldn't consider trying to straighten a drill. They aren't precision to start with and probably couldn't be straightened near enough to drill a hole reasonably close to the original size.

 

[Illinoyance]

I would be tempted to hold the drill in a collet and turn the shank cylindrical.

 

[RJSakowski]

Nothing ventured, nothing gained. If the drill bit was bent, it can be straightened, (within reason). The straightening procures is basically in doing what bent it in the first place. The trick is to determine where the bend is and applying a controlled restoring force. You won't likely get it perfect but you should be able to make it usable. Kieth Fenner has a number of You Tube videos on straightening shafts which would be informative as to technique. He is working on much larger shafting, typically a couple of inches in diameter but the process can be scaled down to suit the need.

When I straighten a piece of shafting, I use two pieces of round stock , one on either side of the bend, to support the shaft and a third pressing down at the bend point. I control either the deflection or the force applied to reverse the bend, gradually working up as I measure the result so as to not over bend. This process has worked well for restoring bent lawn mower crankshafts and mower blades to name a few.

The one caveat is that every time you stretch a piece of steel past its elastic limit, it weakens it slightly. The second bend will weaken it further. If the bend is slight, you should still have enough reserve strength. Even with a catastrophic failure, there more than likely wouldn't be a threat to safety

 

[Ulma Doctor]

Install the drill into your lathe chuck
Indicate the drill for reference, noting the high spot
Using a pipe or a fabricated tube, bend the drill slightly past the lowest indicated low spot and indicate again
Within a few cycles , you should be close enough to make the drill useful again

You could also use a hydraulic press with the drill straddled over 2 blocks to achieve the same result