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Hello,

I have a small plastic building that was assembled with glue from a kit.  I need to drill a hole in the side that will be large, about 3/4 of an inch in diameter.

Given the propensity of thin plastic to split and crack, does anybody have any ideas or tips about how to do this?    I can lay the plastic building on its side on a drill press, but that may not be the best way to go.   Drill presses tend to spin whatever is under them due to their strong torque, and the torque may tear the building apart.

I have regular bits, forsner bits, paddle bits and even key-hole bits.  And, of course, a battery powered drill with adjustable speed, power and clutch.

Does covering the surface with heavy tape before drilling help reduce the chance of splitting/cracking?

Or is this just a bad idea doomed to fail?  :-)

Thanks,

Mannyrock

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3/4 is a pretty good size bit. I would drill the 3/4 hole in something else. Metal would be ideal. But wood would work. If you can clamp it to the side of the building you can use that as a template. Drill a bunch of small holes with a pin vise using that as a guide. Eventually you will have to maybe finish it off with an X Acto saw blade. You can clean the hole up with a Dremel with a sanding drum on low or a round file. It may not be perfect and may take awhile. But you shouldn’t damage anything.

Last edited by Dave_C

I would drill a small pilot hole and then use a step drill bit to enlarge the hole to the 3/4 " diameter you need.

With a new sharp bit, you should be able to just use a battery operated power drill. I would use tape over the hole to help prevent any chip outs, rough edges, etc.

My technique is to move the bit in and out a little bit at a time until you get a smooth pattern going and the right size hole.

Roy, thanks but I can't get a 2x4 in there.  The building itself is only about 2"x 2".

Rattler, your idea was what I was initially thinking about, but I decided that working my way up from a 1/8th bit hole to a 3/4" inch hole would be a lot of bits, and I have found on other projects, using wood, that when you do that, the sides (not the point) of each larger drill bit violently "grab" the sides of the smaller hole as it goes in, resulting in splintered wood and wood chatter around  the edge of the newly drilled larger hole.  So, that may be just too much stress on the plastic.

Dave, I think that your suggestion would work, but it would sure take some time and patience (and I am always short on both :-))   

  I guess I'll try Gary's suggestion of reversing a hole saw, and I'll let you know how it turns out.   I'll tape up the plastic wall in front and back with heavy masking tape first.    I think that it'll either work beautifully, or I'll press a bit too hard and break it.

I just remembered that years ago, I had to drill a large hole in a tile wall, and I bought a key hole bit for tile, which doesn't have teeth on the edge of the cylinder, but instead has an abrasive metal surface, for aggressively "sanding" the edges of the big hole out instead of cutting it out.  Took a lot of time and created a lot of dust, and as I recall it was pretty expensive.  I think it was about a full inch in diameter though, for use in plumbing.

Thanks for all of the suggestions.

Mannyrock

As has been said 3/4 is pretty big.  One of the best investments I have made is a set of number and letter bits.  Steps are much less than fractional bits.  Also when using small steps for soft material like plastic, I use my fingers to turn the bit or a variable speed drill turning extremely slow.  for that size hole the backwards running hole saw sounds good.

Vinyl siding installers often use a circular saw with the blade installed backwards to cut siding.

All the thoughts and recommendations are excellent here.

I have not read about my practice, to place a small sheet of styrene plastic over the space in which you drill.  This uses the same reasoning as the masking tape overlay.  I have used both clamps or a glue to keep the styrene in place.  

The hole saw is the bit I use with a battery drill with the variable speed.  With the variable speed I have not needed to reverse bit’s direction.

The method that I was taught for making a hole in plastic involves using a pair of scissors. You open the scissors up and use only the thin side twisting while applying force gently. First you get a dimple and that opens up to a small hole. Then you shave the sides of the hole with the sharp edge of the scissor blade by continuing to twist the scissors until you get the size hole you want. There is no speed so the plastic never melts.

Mannyrock,

I am not a modeler; however, I have had to make more than my share of holes in different materials. For this effort I would use a hole saw in reverse. By reversing the drill, you will be less likely to catch a tooth, but it will take a bit longer. If possible, try and back the plastic with wood, such as a piece of wood in a vise and then the plastic to be cut on top of the wood allowing you to hold the plastic while drilling down in reverse.

For the price, I'd take a drive over to our/your local Harbor Freight and pick up one of these to do that job...

Step Drill Link

Seems like just the thing to start small, gradually enlarge.  Besides, I've always been intrigued with these bits...never had an excuse to bite the bait.  I'd also reduce the speed as you make the next enlarging step.  Practicing on some scrap piece can also be a good teacher.

Of course, then the bit will just rattle around the workshop waiting for that next one-in-a-million opportunity!

FWIW, of course...

Lots of them on the net...lots of prices, too.

Whatever...

KD

PS...Don't think I'd try a Forstner bit...too big a biting edge.  Methinks it will take a grab and your assembled wall will quickly exit stage anywhere...along with the rest of the structure.

Just a thought.

Last edited by dkdkrd

Thanks for all of the great suggestions.

A complicating issue, here, is that my small building is already glued together, and the hard plastic is pretty  flimsy, so if I put much pressure at all on the outside wall with a drill, etc., the wall wants to bow inward and then break the building apart a the glued corners.  If you squeeze the sides now, you can hear that "crack" sound.

I only paid about $4.00 for this little assembled building, so a total loss of it would be a small loss, but it is just about the perfect size I need for my project.

I have a brand new set of forsners that I have never used, but the package says to never ever use them except in a drill press.  If I put the little building under the press, turned on its side, I would have to hold it in place, and I am pretty terrified of putting my hands anywhere under a drill press that has a forsner bit in it.  You are talking about losing a finger.

I guess that I can try to tape the building down tight on the press plate, and keep my hands away.  And then use the slightest pressure possible.

My drill press in an el-cheapo Harbor Freight, with only two speeds, and you have to move the belt to even do that.

I could also put a small hole saw in the drill press, and run the drill in reverse, and try that.  I would still have to tape it down,. and use really light pressure.

Since my Dewalt hand drill has a really slow speed setting, I guess that I am pushed into using that plus a hole saw, running in reverse.

My drill bits are carpenter bits, so most are only one-sixteenth inch up in size as you go.  I could buy a new set with smaller graduations, but I"ve learned never to buy new tools just to try to jury-rig a really cheap accessory into working.

I have a good dremel, and a few tapered stones, but none of them would make a 3/4 hole.  Maybe if I buy something new, that would be the cheapest thing to buy.

The scissors ideas is very appealing, but I don't think mine would make a 3/4 hole.

John, drilling successively larger holes works for me on hardwood, but my large bits seem to be really aggressive with a fast spin, so that have a bad habit of violently sucking my drill right into the materials with just one or two turns of the bit. Then, you can't back them out.

I'll let you folks know how this turns out.

If I was just dealing with a flat piece of plastic, I think all of the suggestions above would work well, but sadly, I have a sad little building.  :-)

Thanks again,

Mannyrock

@Mannyrock posted:
I have a brand new set of forsners that I have never used, but the package says to never ever use them except in a drill press.  If I put the little building under the press, turned on its side, I would have to hold it in place, and I am pretty terrified of putting my hands anywhere under a drill press that has a forsner bit in it.  You are talking about losing a finger.

I drilled all the holes in my fascia for switches with a Forstner bit, one of the joys of power tools is you don't have to believe everything you read in the manufacturer's instructions.  If I believed everything I read, I probably couldn't use half my tools.  My favorite was all the crap that came on my table saw, how you ever manage to actually use the thing with all that stuff installed certainly escapes me!

I have a couple of the multi-step bits, actually they look like they're made to this job, I'd give them a try.

For nearly thirty years I made my living behind a camera doing product photography. Somewhere along the way I started making sets and props out of plexiglass, Acrylic or Lexan. Many of the trial and error lessons I learned I transferred to my hobbies. If I had to cut several such holes as you describe I would cut a 2 X 2 board around a foot long to a snug fit inside your building. I might use a piece of foam rubber like flipflops are made from and place it over the side of the building. Mark where the hole should be and cut it slightly oversize with a knife then clamp the foam rubber against your building using C clamps and a scrap of plywood cut to approximate the same size as the foam rubber.  Or if you cut it long enough to overhang your building you might screw it to the wood core.  I would precut an oversize hole in both the foam rubber and the plywood before clamping.  Adjust the hole saw bit into position and use the slowest speed the press has and a spray bottle with soapy water to keep it cool. Press the cutter against the piece to be cut in short 1~2 second intervals with very light pressure to keep everything cool and spray the water. I could cut this hole with several devices once the jig held it in place, a cylindrical saw tooth hole saw a paddle bit or an adjustable arm cutter. Once the piece is held rigid cutting the hole is the fun part.   If I were cutting one such hole I would still cut a snug fitting core board to mount and hold the 2 x 2 building steady. Then cut a 1/8" space/ gap on the core right where the hole should be.  I would take a divider with sharp spikes and scribe the circle where the hole should be. Now you have a choice switch to a Dremel tool with a fluted cutter bit and cut by hand  "OR" twist your dividers a couple hundred turns and scribe your way through your plastic wall.  Whatever technique you choose the core of wood and clamping the thing rigidly is the key to a neat hole. One more tip after I scribe a circle on plastic I will run a black dry erase marker over the scribe mark then use a soft cloth to wipe at 90 degrees across the scribe mark makes seeing it with old eyes much easier.  If your building is painted this may not be a good thing. Step bits will certainly make a hole but it may look a bit ragged compared to other methods.  While I like Forstner bits all I have are over 1" and there again are not as neat on thin materials. Guessing the walls of your plastic building are only about 1/16" thick. The fact that you have to deal with an assembled building and not wanting to crush the thing makes the process so much more difficult.    j        

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Last edited by JohnActon
@Fast Mail posted:

Mannyrock,

I am not a modeler; however, I have had to make more than my share of holes in different materials. For this effort I would use a hole saw in reverse. By reversing the drill, you will be less likely to catch a tooth, but it will take a bit longer. If possible, try and back the plastic with wood, such as a piece of wood in a vise and then the plastic to be cut on top of the wood allowing you to hold the plastic while drilling down in reverse.

I agree. Running the bit in reverse will make a scraping/scoring effect on the plastic.  Use a battery operated hand drill with variable speeds for best control. Hold the building down by making a jig.  Piece of plywood for a base and several pieces of 2×4 positioned tightly around the building to prevent it from moving/spinning.  (You said it was 2×2×2 in size. )

@Mannyrock posted:

Thanks for all of the great suggestions.



I have a good dremel, and a few tapered stones, but none of them would make a 3/4 hole.  Maybe if I buy something new, that would be the cheapest thing to

Thanks again,

Mannyrock

Manny......try drawing a circle with something 3/4 in. and using the tapered stone to start and then work out from the center to your drawn lines.

Do you have a photo of the building and the approximate area that needs the hole ?      Why the 3/4in hole ?

Thanks to everyone for every comment and tip! 

Mission accomplished.  Hole Drilled!

After reading all comments, I realized that my project was stupidly unique, because the fragile building was already glued together and the outside walls of the building had fake raised lap boards on it.   So, I found it necessary to use and amalgamation of the of the tips, blended together.  JohnActions latest comments were very appreciated and helpful.

Here is a picture of the building as it started out:



P1020433



Next, you can see that I taped up the wall, inside and out, with two layers of green frog tape.  I used the thin frog tape because I wanted to be able to force the tape down into and between the outside clapboards.    It worked out well.

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Next I cut a really dry 2x2 stake to become 1 3/4 x 1 3/4  with my table saw, and put it in my vise.  The building fit over it, with the wood flush against the inside wall.

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My hole saw had a rather large 1/4 inch center bit, so I did as suggested and drilled a center hole in the building and wood, starting with a 1/16th bit and going up through the sizes to 1/4th.  Then  I inserted the 3/4 inch hole saw in my drill, and slowly ran it backwards.

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It took about ten minutes, running at very low speed with just the pressure of the drill weight, to cut the hole through. I had to take 3 rests.   BIG FLAG here:   Since I have been using drills like this for 30 years, every time I got ready to start drilling again, my index finger instinctively pushed the direction button inward, to run the drill forward, not backward.  I had to catch myself and reverse this, but once I almost forgot!

Then I carefully removed the tape. There were no cracks whatsoever, and just a little bit of white plastic "threads" hanging on in the inside of the hole.  I gently removed those by hand.

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The purpose of my hole is to mount my new large Motion Sensor, which is 5v to 24v DC, 5 amp, with nice 20 gauge stranded wire for input and output.  The sensor fit inside perfectly, and it works great to turn on my Oil Pump and Light when my train passes by.  I only paid $15 for a package of 3 of these sensors.  They are motion detectors to mount on window sills.   I think they are guaranteed for a full year.    I just have to run the wires down through the table through and hole underneath the building, and attach them permanently together.

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Thanks again to all. 

Mannyrock

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Stones soon fill with the plastic, even if run slow, it embeds and wraps around the stone.  A fluted cutter, if not run too fast, will cut without melting the plastic or filling with the plastic. Even when fluted cutters load up it's easy to remove the build up with an old dull X acto blade.  Stones work well with steel and OK with some brass, not so well with aluminum and copper. There are some very hard aircraft aluminum alloys which cut  ok with stones as do some beryllium copper alloys.  Except for Bakelite stones are not very good on most plastic.  Rotary rasps work with common aluminum, copper and plastic though they leave a rough surface that needs finishing with files, sandpaper, wire wheel etc, They are easy to pick clean when they load up. While writing this I recalled something that no one has mentioned that may work well on Mannyrock's task.  Remember the Rotozip cutters they look somewhat like a drill bit but are optimized to cut on the sides. mounted in a hand grinder a 1/8" Rotozip bit would work well.  I would still encourage some method to fasten the 2 x 2 building down.  You will then be able to use both hands to guide the cutter.           j

Glad it worked out well for you. Drilling slowly backwards with light pressure works well on most plastics and also Plexiglass without splitting or cracking, just enough speed to slightly warm the plastic or Plexiglass to soften for easier drilling but not fast enough to melt the plastic. As a former school Custodian and Maintenance I had to do several projects that way, usually worked good.

@Mannyrock posted:

Thanks for all of the great suggestions.

I only paid about $4.00 for this little assembled building, so a total loss of it would be a small loss, but it is just about the perfect size I need for my

I'll let you folks know how this turns out.

@Mannyrock posted:

Thanks to everyone for every comment and tip!

Mission accomplished.  Hole Drilled!



P1020442

Thanks again to all.

Mannyrock



Mannyrock

Great thread  Manny.      Beautiful info and photos on the completed project .   What a great bunch of forumites too.................sometime the returns on 4 dollars can be pretty impresive.

I'm late to this cutfest, but I'll still give you my two cents. I would have drawn the circle the size that was needed on the side. Then I would have used a small drill to drill holes inside the line and around the circumference.  Then a hobby knife would easily cut between the holes to take out the center. Then a bit of filing to smooth the edge.

I do the same when needing to cut out squares, rectangles, etc.

Last edited by Big Jim

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