Let's talk Kerfs (curving your foam)

[GPW]

Page one explains kerfs and spacing ….
Rusty, did you try running your saw blade backwards …

[rustytoolss]

Never thought about running the blade backwards

[rowerwet]

I cut almost all of my foam with a Saber saw.

[KCStudly]

You need a blade with not too many teeth and plenty of clearance for the "chips". The foam cuts so easily that the saw needs to be able to take a chip and eject it. If the tooth count is too high and the chip clearance too low, you won't clear the chip and will start creating friction, which will melt the foam and escalate the problem.

General purpose blade should work. I think, IIRC, I have a 40T Irwin in my table saw. Cuts both foam and wood well.

[lthomas987]

Had I known more about doing kerfs. I would have bought some 1" xps for one section of my roof (2pcs stacked). But not knowing I bought all my foam in 2" thick. I will need to make a 18" inner radius 90 degree curve. I'm going to try this with a piece of scrap 2" foam first. To see how this go. If I don't feel like it's going to work out well. I may have to make my radius in long small sections. Can anyone tell me the spacing for kerfs / and depth of cuts for 2' foam / and number of cuts needed?
Another question I have is. I bought a fine tooth blade for my 10" table saw. Thinking it would give me better cuts in the foam. But I have problems when I cut the foam. The saw will grab the foam , almost like a kick back thing. So I have been using my circ saw instead . I don't get any kick backs with the circ saw.The circ saw has an old general use blade.
Could the fine tooth blade on the table saw be creating my problems ? I actually cleaned off all the foam residew off the side surfaces of the table saw blade thinking that would help prevent the grabbing problem. But it made no difference.

I got a 12" radius in 2" foam. Using a course blade in my table saw. Cuts 1.5" deep.


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[rustytoolss]

Had I known more about doing kerfs. I would have bought some 1" xps for one section of my roof (2pcs stacked). But not knowing I bought all my foam in 2" thick. I will need to make a 18" inner radius 90 degree curve. I'm going to try this with a piece of scrap 2" foam first. To see how this go. If I don't feel like it's going to work out well. I may have to make my radius in long small sections. Can anyone tell me the spacing for kerfs / and depth of cuts for 2' foam / and number of cuts needed?
Another question I have is. I bought a fine tooth blade for my 10" table saw. Thinking it would give me better cuts in the foam. But I have problems when I cut the foam. The saw will grab the foam , almost like a kick back thing. So I have been using my circ saw instead . I don't get any kick backs with the circ saw.The circ saw has an old general use blade.
Could the fine tooth blade on the table saw be creating my problems ? I actually cleaned off all the foam residew off the side surfaces of the table saw blade thinking that would help prevent the grabbing problem. But it made no difference.

I got a 12" radius in 2" foam. Using a course blade in my table saw. Cuts 1.5" deep.
So you had no problem bending a radius on 2" foam ?


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[rustytoolss]

I have a spreadsheet that does all the math for you if you want to give it a try I could share it. It's not well documented at this point but I would be glad to clean it up some next week.

https://docs.google.com/spreadsheets/d/ ... Hs/pubhtml

I found your spreadsheet for doing Kerfs. But I cant seem to make it work. I'm doing a 18" inside radius (90 degrees) in 2" foam. And like you said before cutting 1.5" deep.
How can I make the spreadsheet work ?

[Don L.]

You may know this but just in case, run a few strips of packing tape on the outside of the bending foam board, perpendicular to the kerfs. Pull the tape off once everything is glued and set.
The tape really helps stop breakage.

[lthomas987]

I have a spreadsheet that does all the math for you if you want to give it a try I could share it. It's not well documented at this point but I would be glad to clean it up some next week.

https://docs.google.com/spreadsheets/d/ ... Hs/pubhtml

I found your spreadsheet for doing Kerfs. But I cant seem to make it work. I'm doing a 18" inside radius (90 degrees) in 2" foam. And like you said before cutting 1.5" deep.
How can I make the spreadsheet work ?

There is something wacky with the permissions. I'll sort it out at the office tomorrow.


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[lthomas987]

https://docs.google.com/spreadsheets/d/ ... sp=sharing

Try this link I think the other one was the direct link for me.

[rustytoolss]

https://docs.google.com/spreadsheets/d/1Kk7c9hEz1XWNd5RT-SXk2GimpYZOMOlkoKAXUTULIHs/edit?usp=sharing

Try this link I think the other one was the direct link for me.

Thank you So Much

[OP827]

Note that 1/8"=0.125", just my 2c

[rustytoolss]

https://docs.google.com/spreadsheets/d/1Kk7c9hEz1XWNd5RT-SXk2GimpYZOMOlkoKAXUTULIHs/edit?usp=sharing

Try this link I think the other one was the direct link for me.

I just made a test piece of 2" foam using your spreadsheet information. Works like a charm . Very happy . I will start on the actual roof piece on Monday. Thanks

[lthomas987]

https://docs.google.com/spreadsheets/d/1Kk7c9hEz1XWNd5RT-SXk2GimpYZOMOlkoKAXUTULIHs/edit?usp=sharing

Try this link I think the other one was the direct link for me.

I just made a test piece of 2" foam using your spreadsheet information. Works like a charm . Very happy . I will start on the actual roof piece on Monday. Thanks

I am glad to hear it!


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[twisted lines]

Now on to my question/suggestion. Would a solder gun or wood burning gun (the hand tool you use to burn letters into wood) run at a good temperature to kerf foam?

Both seem to run at round 800 - 900 deg F, or thereabouts from what I've found on the internet.

If that is too hot, you can buy or build regulators to adjust the heat output. http://pcbheaven.com/projectpages/Homem ... ic=worklog

I haven't seen a recommended heat for burning through foam without setting things on fire, if thats even possible.

The issue is not how hot it can get but how quickly it can recover as it cuts. You would need at a minimum a pistol grip soldering gun of around 180 watts or this.

http://www.harborfreight.com/130-watt-h ... 60313.html

Any testers using this tool
Got called out asking for one today Foam again