Question on enlarging a drill hole

[paulga]

I drilled a 1/4 in hole on the closet in the galley to through a 1/4 in tubing. The tubing needs a little bigger hole so I used Dremel 654, insert into the hole then start the Dremel, up and down and around using the bit shaft as a guide. The first few passes were running smooth, and I actually already got a clean enlarged hole to accommodate the tubing. but I tried to further the effort just a bit. Then suddenly to my surprise, the Dremel rotate abnormally crazy like it was stalled by something, and chipped the hole within a second. What is the reason of the strange behavior?

 

[Barking Sands]

LOL....first time? Anytime you put a rotating bit in a round hole you risk this action. And its always a risk. Cant tell you how many times I have tempted fate, being lazy and "extra careful" only for it grab and wind up with that scenario.

 

[magna 6882]

I use a tapered reamer if i need a larger hole in something.trying to enlarge a hole cleanly is a challenge once drilled. The reamer makes quick and clean work of it.

 

[Delta Riverat]

Next time...use a 5/16 or 3/8 follow through the quarter inch.

 

[paulga]

LOL....first time? Anytime you put a rotating bit in a round hole you risk this action. And its always a risk. Cant tell you how many times I have tempted fate, being lazy and "extra careful" only for it grab and wind up with that scenario.

The hole is not in the best location to visually check if the dremel bit is perfectly perpendicular. It must have touched the edge of the hole. I didn't know countersink is also necessary here.

 

[paulga]

Next time...use a 5/16 or 3/8 follow through the quarter inch.

For the smallest hole for a 1/4 machine screw to slide in, should I get 17/64", or equivalently 16mm drill bit?

 

[paulga]

I use a tapered reamer if i need a larger hole in something.trying to enlarge a hole cleanly is a challenge once drilled. The reamer makes quick and clean work of it.

I can see this is used to manually enlarge a hole. Does it still work if you want to keep the hole straight?

 

[Flatswing]

Ok - tubing diameter is usually ID. Try using a step drill to enlarge the hole through a thin partition- easier and cleaner cut.

 

[magna 6882]

The reamers are usually fairly long. Sometimes we will drill a small hole then we can use the reamer to get any angle we want. Straight i easy since there is enough bit exposed to verify its at 90 degrees. Most reamers are made for steel but they work fine in wood. Step bits are sort of a poor mans reamer and work fine for sheet metal but not for accurately enlarging a hole. Best outcome for wood is choose the correct bit to start with but you figured that out already.

 

[magna 6882]

Another idea that just came to me that we use is to drill the desired hole size in a piece of 1 inch stock and place the jig over the hole you want cleaned up. You need to clamp or get a helper and to make sure it dosnt move. Once in place run the same drill bit through your jig advancing in small gentle bumps when you contact the old hole. The jig will quide the bit exactly where you want it cleaning the hole. We use the method then we want multiple holes that overlap. We can drill one hole then move over half a hole and drill again. It only cost you the piece of scrap.

 

[paulga]

i see, step drill bit works on a thin sheet, but he closet wall is considerably thick

 

[paulga]

The reamers are usually fairly long. Sometimes we will drill a small hole then we can use the reamer to get any angle we want. Straight i easy since there is enough bit exposed to verify its at 90 degrees. Most reamers are made for steel but they work fine in wood. Step bits are sort of a poor mans reamer and work fine for sheet metal but not for accurately enlarging a hole. Best outcome for wood is choose the correct bit to start with but you figured that out already.

Thanks.
I mean the enlarged hole will have a tapered shape because the ream is tapered, correct? It cannot keep the enlarged hole straight, e.g. a machine screw needs a straight hole

 

[sean9c]

If it's just a little bit bigger use a round file.

 

[DDW]

You can use the step drill even on the thicker partition. Get the larger hole started with the step drill and then continue with the proper sized regular drill. It is the start of the hole which is usually the problem, once you are in a little bit the drill is guided and doesn't chip the edges.

On the original problem, the closer the cutting bit in a Dremel or die grinder is to the hole size, the more likely it will try to "walk around the hole" and get out of control. Once this happens it is very hard to stop it without stopping the tool completely. When you suspect this might happen, you need to keep a very firm and stiff grip on the tool to prevent it. If the cutting bit is about 1/2 or 1/3 the size of the hole, it is less likely to start.

 

[RT Firefly]

Greetings,
Ms. P. Re: Your post #6. Re-read your chart. 16mm is more than 3X the size of 1/4"!

 

[paulga]

You can use the step drill even on the thicker partition. Get the larger hole started with the step drill and then continue with the proper sized regular drill. It is the start of the hole which is usually the problem, once you are in a little bit the drill is guided and doesn't chip the edges.

On the original problem, the closer the cutting bit in a Dremel or die grinder is to the hole size, the more likely it will try to "walk around the hole" and get out of control. Once this happens it is very hard to stop it without stopping the tool completely. When you suspect this might happen, you need to keep a very firm and stiff grip on the tool to prevent it. If the cutting bit is about 1/2 or 1/3 the size of the hole, it is less likely to start.

Thanks.
The examples of chipped edges on the internet are not as bad so I didn't know it's a big risk. I would buy some odd sized drill bit to make it in one go.

 

[paulga]

If it's just a little bit bigger use a round file.

Do you mean working the file around the hole to bite off the edges gradually?

 

[sean9c]

Do you mean working the file around the hole to bite off the edges gradually?

I mean stick the file in the hole and rub it around to make the hole larger.

 

[magna 6882]

The reamers i use are only tapered art way so you start the hole with the tip of the reamer and the flutts on the reamer go straight a third of the way up cutting a straight hole.

 

[High Wire]

The teeth might have dug in and propelled the bit around the edge of the hole. Hard to say what actually happened.

 

[Larry M]

Bummer. Free-handing a router bit is hard on the best of days. If I had to guess, the bit came loose?

You can maybe dress up the hole with a thin piece of round circular brown plastic or wood with the your hole drilled in the center? I’ve had key hole saws walk across wood before that I’ve had to repair.

 

[paulga]

Bummer. Free-handing a router bit is hard on the best of days. If I had to guess, the bit came loose?

You dress up the hole with a thin piece of round circular brown plastic or wood with the your hole drilled in the center. I’ve had key hole saws walk across wood before that I’ve had to repair.

It didn't come loose. The manual says to insert the bit as far as possible into the collar. I inserted only half the shank into the collar to have more insertion length into the hole. I noted the shank was pushed into the collar for a bit when the adversity happened

 

[DDW]

When a bit gets out of control and starts running around it like that, the bit can quickly work its way in or out of the collet. That situation is hard on everything, not just the hole. The key to prevention is rigidity (a tight hold and control of the tool), and bit clearance (hole ~2x or more bigger than bit). You can get away with less clearance but really need to control the tool well.