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Author Topic: Carvex - burning and bending blades when cutting 140mm radius circle in MDF?  (Read 2367 times)

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Offline eddomak

  • Posts: 276
I am using the cordless Carvex with the circle cutting attachment to cut a 140mm radius circle in 9mm MDF, in an anti-clockwise direction. All seemed to be going fine for a while, but then I got a lot of burning and the blade bent. One new blade later the same result.

I have cut (much) larger circles in plywood before with no problems, so was wondering if anyone could shed any light on this? Perhaps the blade is too wide for that small radius? Bad technique and introducing some side play? Faster or slower speed of blade? Faster/slower forwards motion?

Thanks?

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Offline SRSemenza

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Which blade type are you using?    FS, FSG,etc?

Seth
« Last Edit: November 20, 2017, 10:28 PM by SRSemenza »

Offline aloysius

  • Posts: 199
You're correct.  That "wide" blade is trying to twist inside the tight radius kerf.  In protest, friction against one or both of the blade guides is introducing heat, ruining temper & sharpness, which serves to exacerbate the problem.

For tight radii, there's a couple of alternatives:  very narrow rear-offset scrolling type blades, or a relieved kerf V-section Cunex blade as is unique to Mafell's P1 saw.
FOG-wit since '95:  Some say since birth...

Offline Holmz

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...  In protest, friction against one or both of the blade guides is introducing heat, ruining temper & sharpness, which serves to exacerbate the problem.
...

Hence the term "ill-tempered"... ?

Offline Peter Parfitt

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There are a couple of possible things going wrong.

The first, picked up above, is that your blade must have sufficient set to allow free movement along the curve. The narrower the blade the less set is required.

The second is to make sure that you are using the circle/trammel feature correctly. It is possible to put the trammel pivot in the wrong hole which would cause a binding action as the blade would then not be at a tangent to the circle that is being cut.

The trammel appears from about 7 min 40 sec in this video:



Peter
« Last Edit: November 21, 2017, 04:22 AM by Peter Parfitt »

Offline ToddTurnerT4.75

  • Posts: 11
I had the same problem with mine-no matter what I was trying to cut. You should tighten the blade guides located near the bottom of the blade. It takes an Allen wrench. For me, problem. solved. Now I love my carvex, whereas I was considering selling both.
Festool & Powermatic!

Offline Gregor

  • Posts: 582
You should tighten the blade guides located near the bottom of the blade.
It is  indispensable to set the blade guides every time you switch the blade to a different type.

Doing it might take a little moment of your time and possibly be annoying - but it's that setup that will make the carvex a precise tool you'll love to use.

Not doing it will waste blades (with the guides set to close friction will heat and toast the blade, quickly) and/or possibly quite expensive stock (when the guides are not guiding the blade can, and most likely will, wander).

Offline Holmz

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I have not seen anyone recommend the blade that the fine fellow from Sydney should be using. Is there a particular blade that would help?

Often there can be a tone of user error, but I think some recommendations of a few blades could be worthwhile.

Offline Michael Kellough

  • Posts: 3021
I have not seen anyone recommend the blade that the fine fellow from Sydney should be using. Is there a particular blade that would help?

Often there can be a tone of user error, but I think some recommendations of a few blades could be worthwhile.


Spyder blades. Might wreak havoc with the blade guides...


Not as familiar with Festool blades but this Bosch T101AOF should do.

Offline rst

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I'm with Micheal, the Bosch T101OAf is my go to blade.  I cut plastics more than anything else, speed set to 3.  Cuts anything up to 3/8", works tight radius', and does not bind up or melt as long as the speed is low enough. 

Offline Holmz

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...

Spyder blades. Might wreak havoc with the blade guides...


I measured the Spyder blades I have in the assortment pack.
The 300010, 3000011, 300032, and 300017.
The all measure ~1.5mm at the front kerf side and between 1.46 and 1.48 on the tail end.
So they are like a dragster... fast-n-straight.

Like ObeWan says...
"These are not the blades you are looking for."

Offline SRSemenza

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No tone of user error here but it would also be helpful to know which blade @eddomak was using when the burning occurred. Trying to narrow down the cause.

Seth

Offline Peter Parfitt

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Although you can use rectangular section blades in the Carvex the new Festool ones, recommended for the machine, have a trapezoidal (or tapered) cross section.

Peter

Offline eddomak

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Thanks all for the suggestions, sorry I haven't replied as it was a busy weekend out of the workshop.

I was definitely using the correct side trammel point for the hole centre, so at least that was good!  [big grin]

I still don't have an proper answer yet as to which exact blades I was using I haven't had time to check, but at first I was using a Vermont American blade that was quite thin, and had a long run-out, then I switched to a Festool blade for tight curves (similar to S50/1.4K ):


I had more success once I got rid of the waste side and did some manual cutting without the trammel, as the new blade kept following the old cut line and being guided badly into exactly the same type of skewing/bending action the previous cut had sent.

To be honest, as it is a very simple project and not critical I will be just manually cutting and sanding to the line, but I sure am glad I did this on an MDF template rather on the final piece.

Thanks again! I will report back once I have the blade specs.


Offline Cheese

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I still don't have an proper answer yet as to which exact blades I was using I haven't had time to check, but at first I was using a Vermont American blade that was quite thin, and had a long run-out, then I switched to a Festool blade for tight curves (similar to S50/1.4K ):

That's interesting...because the S50/1.4K (486564) blade is the last blade I'd use for this application inspite of Festool's recommendation. I think Festool meant this blade to be used for free-form scroll cutting where perhaps you cut left, then you cut right and then you cut left again. This allows the blade to flex left, then flex right, then flex left again and because it is free-form cutting, you'll never really see how much this blade deviates from being perpendicular to the cutting surface. Whereas when cutting circles, when you start the cut it's perpendicular to the surface, however as the circle cutting progresses, the blade gets bent further and further towards the center of the circle. Once you've gone 360ยบ, you can see a definite demarcation line between the initial cut and the final ending point. This blade while only .178" (4.5mm) wide (a good thing) is only .035" (.89mm) thick and has a kerf of .042" (1.06mm). That's only .0035" clearance per side.

A better choice would be the S75/4 FSG (486551) which is .305" (7.7mm) wide but is .050" (1.3mm) thick and has a kerf of .082" (2.1mm). That gives you a side clearance of .016" per side. That's huge, relatively.

Having said that, I've tried cutting tight radiuses (1.75") with the S75/4 FSG in a Mafell P1 cc. The blade still bent and the cut was not perpendicular to the surface. The only blade that worked for me was the Mafell Cunex W1. It has a width of .296" (7.5mm) is only .042" (1.1mm) thick yet has a kerf of .117" (3.0mm). That yields a side clearance of .038" per side.

Offline Gregor

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I would suggest to try with increased orbital motion (the 0-3 twist knob at the front) and be really slow with the feed rate to give the blade time to cut where it should, instead of directly jumping into (and then being guided by) the little but misplaced kerf it just made with the last stroke.

Offline eddomak

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I would suggest to try with increased orbital motion (the 0-3 twist knob at the front) and be really slow with the feed rate to give the blade time to cut where it should, instead of directly jumping into (and then being guided by) the little but misplaced kerf it just made with the last stroke.

Thanks for that suggestion - compared with last time (a much larger radius) this time I also only had orbital action set at 2, and not 3. for curiosity's sake I might end up giving it a go (and risk wasting another blade.  [unsure])

Offline SRSemenza

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I would suggest to try with increased orbital motion (the 0-3 twist knob at the front) and be really slow with the feed rate to give the blade time to cut where it should, instead of directly jumping into (and then being guided by) the little but misplaced kerf it just made with the last stroke.

Thanks for that suggestion - compared with last time (a much larger radius) this time I also only had orbital action set at 2, and not 3. for curiosity's sake I might end up giving it a go (and risk wasting another blade.  [unsure])

I haven't cut all that many curves but using orbital in a tight curve seems the opposite of what would work, to me?

Seth

Offline Cheese

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If memory serves me correctly, and that could be an issue  [smile] , when cutting tight radiuses with the Trion, Carvex and P1 cc, the orbital action was set at either 1 or 2.  As Gregor suggests, one of the most important issues is to slow down the feed rate of the jigsaw and let the blade do its job. I take a feed, cut, clear approach. As in feed the saw slowly, let the blade cut and then let the blade recenter/realign itself and finish clearing/cutting its own kerf. That seems to work the best.

Offline Gregor

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I haven't cut all that many curves but using orbital in a tight curve seems the opposite of what would work, to me?
Depends on how you look at it: On one hand orbital free should give a cleaner cut (especially the outer kerf), on the other hand high orbital should give the saw more chances to eat away at the inner side of the kerf instead of wandering outward in it... Havn't made that much science on this particular topic myself so it's more anecdotal at this point (but it worked for me).

However, slowing down should definitively help lessen the problem with the blade wandering.

Offline SRSemenza

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     OK, I made some circle cuts just to see how it would go.  1/2" MDF.  Carvex with Festool FSG Carvex  blade. The blade was used to start with.  Zero orbit. Feed rate .... pretty much a fast as I could go on the two larger ones. The smallest I slowed down a bit. I don't think it took more than 15 - 30 seconds on any of them. No burning on either side of any. In the pics the dark areas are just shadow.  The largest is about 5" diameter using the circle cutter. The others are about 2 1/2" and 1 1/2" diameter free hand. I got a little sloppy on the free hand but some parts of the curve are even tighter than the diameter due to that.  No difficulty , zipped right through.







Seth

Offline eddomak

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     OK, I made some circle cuts just to see how it would go.  1/2" MDF.  Carvex with Festool FSG Carvex  blade. The blade was used to start with.  Zero orbit. Feed rate .... pretty much a fast as I could go on the two larger ones. The smallest I slowed down a bit. I don't think it took more than 15 - 30 seconds on any of them. No burning on either side of any. In the pics the dark areas are just shadow.  The largest is about 5" diameter using the circle cutter. The others are about 2 1/2" and 1 1/2" diameter free hand. I got a little sloppy on the free hand but some parts of the curve are even tighter than the diameter due to that.  No difficulty , zipped right through.
Seth

Thanks Seth! I feel a little guilty as I am the OP and still haven't reported back yet  ::), but trust me, it was on my mind as I was doing the other DIY jobs around the house.

I have cut much smaller radius curves in the past freehand, with lots of different blades, so was very surprised when this happened. Oh, well, I promise to come back with some results soon.


Offline Fogy

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For circle cutting, try mafell P1CC ..

Offline Peter Parfitt

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The Carvex is perfectly capable of doing what the OP wants.

Peter

Offline ben_r_

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Circles that size and depth Id rather cut out using a router and circle cutting jig. Im my case Id have used the OF 1400 with the Micro Fence Circle Jig.
If at first you don't succeed, redefine success!