make a bigger hole

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mikeblas

[H]ard|DCer of the Month - May 2006
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Jun 26, 2004
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I hope ya'll will entertain my non-case related metalworking question... I'm sure someone here has done some similar machining to their case, or in a case fabrication project.

I'm replacing the gauges in the dashboard of my boat. I've got five gauges to replace,

The old gauges have an OD of about 1.920, and the new ones have an OD of 2.020. The dash panel material is steel that is about 0.100 inches thick.

Today, I used my Dremel to widen the hole for the first gauge. It took about an hour, and I ate up a few different bits. I burned through a whole battery, too. I've widened holes in other materials--even steel, though much thinner gauge--this way, with great results. This is proving pretty hard, though.

I know I can't use any sort of hole saw or drill, since the existing hole is already so close in size to my desired hole size. I'm happy to do it free hand, and because of the way the gauges mount the hole doesn't have to be very perfect. But the Dremel is slow going.

I have a cordless drill that I can take down to the boat, but I don't know what kind of bit I could get for it, or the Dremel, to make easier work of opening the holes.

What tool can I use to best increase the hole size?
 
Use a hole cutting router jig. I recommend the Jasper 400.. it's fantastic. Though you have to glue a piece of wood to the back of it because it uses a centerpin.
 
id say stick with the dremel but get better bits and try varying speeds. faster isnt always better. if youre only taking off that much then i dont recommend buying a whole array of tools just to do this once. have you been using sanding drums or cutting bits or what? i think if you try some pretty heavy grit grinding stones it shouldnt take too long. do you have a corded dremel? theyre soooooooo much better than battery ones. if you dont have one can you get a corded drill or a compressed air powered grinder? those would both give you some more power as well.
 
Ideally, I could remove the dash panel from the boat. But it is boating season, and when it's not boating season, it's rainy. I'd like to do the job in place. Anything that requires a center pin is right out, too, since anchoring the center in an existing hole is not practical, particularly in-situ.

Since I don't have power at the dock yet, corded tools are out.

I went through various grinding stones. The metal melted to the stone, and I used about three stones. I had some generic diamond grinding bits, but the work also ripped the abrasive off the cutting surface pretty quickly. (I had used these bits on thinner metal without a problem.) These made more progress than the grinding stones, but I still used two--on that same hole.

I ended up using a Dremel 100 bit, and this made great progress, but is very small--it's cutting surface isn't even as thick as the metal. As such, I had to move it around a lot and it skipped out a couple of times, scarring the face of the dash. (FUCK!) Looking through the catalog, there's some barrel-shaped cutters that I'll try, and they're available in HSS and tungsten, so maybe they'll last a while and cut more efficiently. The #9901 looks good, for example, though I'd like a larger diameter head to help get a smoother circle.

I'm not beyond buying a good tool, even if I only use it for the four remaining holes. I can always sell it on Craigs List or eBay and recoup some money...

Thanks for the advice; please do let me know if you have any other ideas.
 
go slow then. :p either use a slower speed or less pressure. sounds like you dont mind giving up a bit of time to do this. this will kep the metal from melting onto the grinding bit. also make sure you have a nice heavy grit. you can also do a bit on one side of one hole, then switch to the other side, then switch to the next hole, then come back, etc to try to spread the heat out and let it dissipate instead of grinding on one section for a long time. good luck!
 
I think the stones are too fine for this use. I found some of the Dreme #9901 heads that I wanted, and I picked up a couple of Dremel #115 heads. I think these will do well, but we'll see over the weekend.

Thanks for your advice!
 
Wouldn't it take forever to sand off that much material?

0.05 sounds like only a little, but on that size hole, it's more than 0.03 cubic inches of material. Five holes is going to be .15 cubic inches total.
 
mikeblas said:
Wouldn't it take forever to sand off that much material?

0.05 sounds like only a little, but on that size hole, it's more than 0.03 cubic inches of material. Five holes is going to be .15 cubic inches total.
Click to expand...

thats why hes grinding not sanding. :D
 
Another option is to draw out the needed hole size on your material and use nippers to remove the bulk of the material then finish it off with the sanding drum.
 
I can't find a nibbler (if that's what you mean by "nippers") that will handle 10 gauge steel. Well, I can; but they run on 120 volts (not available at the boat) and cost almost $400. If you really do mean "nippers", I'm not sure how I'd get a scissors-shaped tool inside the hole, in the dash panel, in order to actually use it.

ekuest said:
thats why hes grinding not sanding. :D
Click to expand...

Who's he that's grinding? Me, isn't it?
 
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Yes nibbler is what i meant to say.

Maybe you can rent a nibbler and a small generator for a few hours to get the job done, check some local tool rental shops, using a dremmel will take forever and then some.
 
It took an hour to make the first hole, even with all the problems I've outlined in this thread. Now that I've got more appropriate bits, I think I'll be able to make better progress. I'll report back about it; if the rain stops, I can spend some time on the project on Saturday.
 
If you have not had any luck yet you could find metal grinding bits for an air powered die grinder. you can chuck them in your drill, they should be by the air tools in your closest hardware store.They come as small stones mounted an a shaft and have different grits and can remove alot of material so be careful if you go this rout.
 
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Why not just use a cross-hatch half-round file? If you can get good pressure on it, it should only take about 15 mins per hole to expand it. Costs about $10 or less for a good one.
 
46564v.jpg
 
I don't have any files which would be appropriate. The large files pictured above are too wide to meet the inside radius of the hole. I don't have any hal-round files at all, I don't think; and even if I did, I wouldn't have thought of using them on such thick plate.
 
I would? I figure an inch-wide half-round file would fit great; the hole's radius is 2 inches.

I ended up finding an aluminum-oxide grinding point at Home Depot, which worked great ... mostly. After unwrapping it, I found that it was defective, with a runout of about an eigth of an inch. I used it anyway, though it would skip and grab substantially unless I was very careful to balance against it.

Using the griding point to remove most of the material and a Dremel #115 cutter head to clean up, I got through the other four gauge holes in about 90 minutes and spent the rest of the afternoon wiring. Had I not marred the face of the panel when the Dremel skipped, it would be perfect. Even with the scars, it's a huge upgrade for the boat.

Thanks for your help, ya'lls!
 
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