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Aimerino
04-11-2002, 01:57 PM
Hi everyone-

I am wondering if anyone knows a good way to cut Hardibacker into a circular shape. I know that you're supposed to score and then break off the piecec you're working with, but my project is a little more complicated because of the curve. Is there a particular type of saw that would be appropriate for cutting the board?

Thanks for all of you!

Amy

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Bartj
04-11-2002, 02:25 PM
Amy, you'll hear from the pro's, but this is how this rookie did my latest project. I used a masonary blade in a jig saw and it did just fine. I also use a masonary blade in my circular saw with the same results. BTW, I also cut 12 x 12 tiles with the same blade. (All outside of course. Dusty.) I have also drawn a line and then drilled holes along the line about every 1" with a masonary bit and knocked out the center with a hammer. Not as clean a cut, but it worked for the toilet flange opening.

Bart

Aimerino
04-11-2002, 02:42 PM
Thanks, Bart, that is really helpful. That makes sense that a masonry blade is the way to go. I like the idea of drilling a hole every so often. Isn't the circular saw going to have problems cutting out a circle that is 4' in diameter, though? Thanks again.

Amy

Harry
04-11-2002, 03:21 PM
What I do is on the side to be tiled I mark my circle ... score with the carbide tip tool used for the job (utility blades don't work well) .... make an X in the center of the circle and from the other side give it a blow with a hammer. Takes about 30 seconds.
I don't know what the "scoring tool" is called but I saw them in Home Depot the other day.

Harry

John Bridge
04-11-2002, 03:43 PM
Hi Amy, (Harry, she want's to keep the circle. ;) )

Bart had the best plan. It would be slow, but you could do a clean job with a jig saw and a masonry blade. You would have to let it cool every so often, but you're not in a rush, are you?

John

Rob Z
04-11-2002, 04:34 PM
Harry

I haven't used Hardi, so I don't have an answer for this...will a Roto Zip with cement board bit cut Hardibacker?

Harry
04-11-2002, 04:43 PM
Keep the circle?? .... so much for my brilliant idea :D
Rob ... never tried the Roto Zip, but it should work great.

Rob Z
04-11-2002, 05:00 PM
LOVE my roto Zip! :D

Tom
04-11-2002, 07:21 PM
A rotozip will cut through like butter. If no rotozip's available, or if dust is a problem, score your circle with a carbide tipped knife and score straight lines from the edge of the circle to the outside of the board. support the circle that you're keeping ant knock out each of the sections you created with a hammer and 2X4. If you score your circle well, Hardibacker will break off clean.

Bri
04-11-2002, 07:27 PM
Hi
Mini-grinder with a dry cut diamond blade works great...4 inch blade allows for cutting a nice radius.Dusty?...YES!

Aimerino
04-11-2002, 07:58 PM
Thanks everyone! I think that you've all given me enough to go on. Your suggestions will come in very useful I am sure. I don't know what a Rotozip is, but I'm going to look into it. I like the idea of scoring the circle and then radiating scores from the circle to the outside of the board and then breaking the sections off. I am sure that something will work. (Not your suggestion, Harry. Sorry) Thanks again!.

Amy

Jason_Butler
04-11-2002, 09:27 PM
Gotta go with Bri on this one. A 4" grinder with a diamond blade works wonders for circular shapes in CBU and tile of all flavors

Jason

Bartj
04-12-2002, 02:07 PM
Amy, I only used the circular saw when I had to cut a corner on the hardibacker. Complete straight cuts were the score and snap. However, I did use the circular saw with the metal masonary blade to cut the half moon shape on two 12 x 12 tiles that butt around the toilet flange. I marked the semi circle with pencil and took straight cuts right up to the line about 1/2" apart. The tile cut and broke away very close to, and following, the pencil line. I nibbled away a couple of ruff spots with the blade. It worked very well. I also cut out an opening on two tiles for around the floor vent. I made two cuts into the tile with the circular saw and then scored a line across with the tile cutter blade and snapped the piece out. This worked well too. I did the cutting outside on a portable workbench. I used a C clamp and piece of soft wood for blocking to hold the tile down. WEAR EYE PROTECTION. Goggles are best.

davefoc
10-31-2006, 01:21 AM
I'm no expert but I have tried most of the techniques suggested. My comments:

4 inch grinder with a diamond blade:
Works great except it makes huge quantities of dust and the hardibacker site has some really gnarly warnings about the danger of the dust.

Rotozip:
I was surprised to see somebody recommend this. I bought a special carbide blade that was fairly expensive ($10 bucks or so) as I recall. It worked fairly well but by the time I was done with the cut the blade was shot. And I varied the height so I could use different sections of the blade. Maybe I bought the wrong blade?

Masonry bit on a jig saw:
I haven't tried this but I'm cutting out a sink opening tomorrow and I think I'll give it a shot.

Drill and punch:
Ugh. Slow and an ugly hole. But less dust.

Scribe (carbide blade) and bang out the section:
I haven't tried this. On 1/2 inch material it seems like it might be really hard but on 1/4 inch maybe it works ok. Harry must be the man when it comes to scribing.

Scribe (utility knife):
A non-starter I think. Utility knives just don't work very well on hardibacker.

ETA: I was just looking at ads for power shears to cut hardibacker. Reading the warnings about the dust have inspired me to change my ways and be more careful about the dust created from cutting hardibacker. I liked the looks of one product that attached to your drill. Unfortunately, it was about $120 bucks and that was more than I felt like spending. I also noticed that there are special fiber cement blades for your circular saw that supposedly reduce the amount of dust created.

Does anybody have any comments about these options. It looks like the shears would be great for circles and other odd shapes.

sandbagger
10-31-2006, 01:57 PM
Masonry bit on a jig saw: I've used one described as a "carbide grit" that works pretty well - about 5 bucks at Homer's. Have not tried it with my Rotozip, but I was cutting straight lines so the jigsaw was a better match.

Heed the dust warnings! Wear a good mask and keep the dust out of your eyes. Do it outside if possible and stand upwind. If you can, have a helper hold a shop-vac nozzle near the blade as you cut.

go slow or you'll scorch the blade. :goodluck:

davefoc
10-31-2006, 11:50 PM
I cut out sink holes in two 1/4 inch hardibacker panels today.

On the first I used the masonry bit on a jig saw idea. It worked great until about 2 inches from the end and then blade fell out of the saw and it wouldn't stay in. It was an Hitachi blade with carbide bits. The shank was very soft. I've never seen this happen. Anyway I finished up with a regular rough wood bit and that worked fine also but I don't know how long it would last.

I used the score and bang it out technique (Harry's idea) on the other panel. I was surprised at how well that worked. It did produce a pretty rough hole though, maybe my technique wasn't the greatest.