Replies

1. 
   WoodyAl | Apr 21, 2009 02:08am | #1

   I haven't tried that but I think what's happening is the jig saw is trying to cut a straight line or track to the outside of your circle when the blade is bending outward and bending the opposite direction when you are over-compensating to get it back on track.

   It may be better to draw the circle on the plywood and then simply cut slightly proud of your line by freehand with the jig saw. Then trim to your line by sanding.

1. 
   polarchip | Apr 21, 2009 09:06am | #7

   hi WoodyAl,

   What you say could very well be happening.  But what I've found so far is that the results vary depending on what type of blade I've used.   For example, I've tried the Makita #10 blades.  In order to fit them into my jigsaw (variable speed Dewalt 313) I've had to file them down a bit.  Results not good.  With Vermont America blade, although blade was not new, results were the worst.   The "Master Mechanic" brand blade with 10 teeth per inch gets me better results then the other blades I've tried. 

   JJ

    

2. 
   mike4244 | Apr 21, 2009 02:12am | #2

   The blade is heating up and then warps as you cut. Try Bosch Progressor blades, these seem to last a long time. If the cut has to be perfect you can use a router in the same way you are sawing. If the diameter can be slightly smaller than 8'-0",then use the router to clean up your previous cuts. You might wind up with 7'-11-7/8" or so instead of 8'-0"radiuss.

   mike

1. 
   polarchip | Apr 21, 2009 09:15am | #8

   hi mike4244,

   If I can find the Bosch blades, I'll give them a go, because I'm trying to keep my rig on a budget. 

   JJ

3. 
   Dave45 | Apr 21, 2009 02:14am | #3

   Rough cutting followed by sanding is probably your best bet. Jigsaws are handy, but eliminating the blade flex is almost impossible.

1. 
   polarchip | Apr 21, 2009 09:23am | #9

   hi Dave45,

   Yep, it's been an education so far.  But nonetheless, what I've found so far is that some blades work better then others.  

   JJ

4. 
   JMartinsky | Apr 21, 2009 02:23am | #4

   Dear JJ,
   Try a router with a straight bit. Start with a shallow pass and then 1/8" at a time or so, increase the depth of your cut.

   Best,

   John

1. 
   polarchip | Apr 21, 2009 09:30am | #10

   hi Jmartinsky,

   I certainly intend on using a router with a straight bit, but would dearly love to keep my rig on budget.  Will try to find the Bosch brand jigsaw blades as others have suggested and give them a go.

   JJ

1. 
   JMartinsky | Apr 21, 2009 03:39pm | #15

   Dear JJ,
   Well, if you intended to hit it with a straight bit, then you might as well go for it. You could do as suggested and do the initial cut out with the jigsaw and use the same rig for the router. I have made temporary bases out of plywood or plexi. Just leave some excess somewhere. Or make the base in the shape of, say a tennis racket, using the "handle" part to attach to your existing circle cutting rig.Best,John

1. 
   polarchip | Apr 21, 2009 05:14pm | #16

   hi Jmartinsky,

   Woops....improper wording on my part.  What I meant to say was that I would dearly love to get the job done with my jigsaw circle cutter rig and only go to the router as last option...the main reason being to avoid ( or perhaps delay) the purchase of a router & bit assortment.

   JJ

1. 
   JMartinsky | Apr 21, 2009 09:51pm | #21

   Dear JJ,
   Well, let me simply suggest to you that this is the PERFECT time to make such a purchase! I would suggest Bosch:http://www.amazon.com/Bosch-1617EVSPKBP-Combination-Plunge-Router/dp/B000BGKIJ6/ref=sr_1_2?ie=UTF8&s=hiqid=1240339685&sr=8-2That is a terrific set up and I would suggest a Bosch, Ammana, or Freud bits. I have the older PC 1 1/2hp plunge router, which is nice, but sort of clunky. The Bosch routers are much nicer.Best,John

5. 
   saschafer | Apr 21, 2009 04:42am | #5

   Bosch has a new blade design out that you may want to try; the model number is T308B. (You should be able to find them at home centers.) It's supposed to cut very cleanly and smoothly, which should help.

   But you do have to face reality: A handheld jigsaw is not the most precise tool in the world, so expect to do some clean up afterwards. If you don't have a router, cut the circle a hair oversize and sand to the final radius.

   -Steve

    

1. 
   polarchip | Apr 21, 2009 09:33am | #11

   hi saschafer,

   Will keep an eye out for Bosch T308B.  In all probability, will need to get em via mail order.  Will let you know how they work out.

   JJ

1. 
   RonInOttawa | Apr 21, 2009 08:13pm | #20

   Lowes carry them. About $14 for a pack of 5. Once you try them you won't look back at the ones you are currently using!Regards,Ron

   Edited 4/21/2009 1:13 pm ET by RonInOttawa

6. 
   roc | Apr 21, 2009 04:53am | #6

   You didn't say what jigsaw. Gosh I hate cheep single speed jigsaws ! ! ! Unless you like noise, vibration and cuts where the saw has a mind of it's own then you will love them.

   I use a high end variable speed DeWalt that is a pride and joy. I cut steel with the thing ! ! !

   Running it slow keeps the heat down. I agree the high end blades are great. You may want to try to find some blades with some "set" for cutting the curve. Touch the warm blade now and then with a chunk of wax to keep the friction down.

   Strongly recommend a bandsaw for this task. There are a few New Yankee Workshop episodes that show Norm doing this.

   Wow you just joined today as well as first post.

   Welcome !

   Hey put up some info if you will on your public profile. What you like, what you do, heros what not.

   roc

   Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )

   
   

   ---

   Edited 4/20/2009 9:56 pm by roc

1. 
   polarchip | Apr 21, 2009 09:39am | #12

   hi roc,

   I've seen Norm on the New Yankee workshop use a bandsaw for circular cuts.  Bandsaws certainly do get you superb results.

   JJ

7. 
   davcefai | Apr 21, 2009 09:57am | #13

   As has been pointed out above, the physics is working against you.
   If you were freehanding you would twist the saw a little into the cut to widen the kerf so that you can turn the blade. (This is, I think, intuitive, you might not even notice that you are doing it.)

   Is it possible to mount the saw so that you can control the twisting as you go around?

   I have found that saw blades vary from 0.8 to 1.2 mm thick. The thicker ones may behave better. I would guess that coarser blades would also cut a wider kerf but your tearout would be terrible.

   Frankly I think that your best bet is going to be to rough cut as you are doing, then go round with a router mounted the same way.

1. 
   Lataxe | Apr 21, 2009 11:25am | #14

   Dave,

   "Frankly I think that your best bet is going to be to rough cut as you are doing, then go round with a router mounted the same way".

   I would agree with that - except for the "rough cut as you are doing" bit. :-)

   I've cut a number of round tops using a piece of wood with a router at one end and a pin at the other albeit only one was in 3/4" plywood (the rest were in various hardwoods up to 1" thick). 

   Best results come from:

   * multiple circuits, gradually depthing the bit by around 1/8" until it's a mere hairsbreadth from cutting through to the bottom of the workpiece;

   * use of a 1/4" downcut spiral bit, which leaves a very clean top corner, a clean wall (because the bit is always in contact with he workpiece) and doesn't require too much wood-removal/work to do the cutting.

   I do the job on a full sacrificial sheet of cheap plywood, in case the bit does break through on the last pass.  When the circle is attached only by that hairsbreath of remaining wood, I snap the circle out by pulling up the waste.  Any slight raggy bits left of the hairsbreadth are sanded off with a couple of swipes of a fine sanding block.

   The advantages of the router method are that it's quick and leaves a fine finish.  If a sawn edge is going to have to be cleaned up with a router after jigsawing it, why bother with the jigsaw?

   Lataxe

2. 
   polarchip | Apr 21, 2009 05:21pm | #17

   hi davcefai,

   Regarding physics working against me.....this may be so, but for the life of me I can't piece together why some blades bend to right while others bend to the left ...without any modication whatsoever to my rig, & yet while other blades yield better results.

   JJ

1. 
   davcefai | Apr 21, 2009 07:17pm | #19

   I had this problem recently ( on straight cuts ) and, just before taking my jigsaw in for repairs I discovered that the blades were only 0.8mm thick. Depending on which way they went into the blade holder they were angled to one side or the other.FWIIW these were Blackspur blades. Wolfcraft are 1.2mm and do not give me a problem.

1. 
   polarchip | Apr 23, 2009 01:26am | #27

   hi davcefai,

   I think you hit the jackpot.....if my Dewalt jigsaw accepted blades 2mm thick and the aforementioned were available (especially in a high quality hardened steel/alloy), me thinks this wabely blade problem with jigsaws would be a non issue,

   Will check out Wolfcraft blades,

   JJ

8. 
   mr_kramer | Apr 21, 2009 06:00pm | #18

   You may be pushing too hard too fast for that dense thichness. Turn your blade speed up and push from the rear of the saw. Instead of holding the handle to push it along, just hold the saw down, push from the rear and let the saw chew as much as " it " wants to. Also Bosch offers saw blades that cut on the downward stroke. That will help.

1. 
   polarchip | Apr 23, 2009 01:16am | #26

   hi mr_kramer,

   thanks for the suggestions....turn the speed up, push from the rear while holdding jigsaw base to wood & let saw do the cutting......will give it a go,

   JJ

9. 
   zolton | Apr 22, 2009 01:23am | #22

   JJ,

   I wonder if the blade deflection you're experiencing doesn't have something to do with how the plys are laid up in the sheet goods you're cutting. The difference between cutting with the grain through some of the plys as opposed to across the grain would have some influence on how the blade behaves. The grain orientation within the sheet's core plys change frequently as you made your way around the circle..

   Another thing to keep in mind is that jigsaw blades (at least the less expensive ones you're using) aren't all that precisely ground. It could be that your blades are cutting more aggressively on one side than the other due to inconsistent manufacturing. For reference to this problem, ask anyone who has had a handsaw sharpened by a filer who leaned a little more to one side than the other! Such a handsaw cannot be made to cut straight to a line.

   Zolton 

    

   If you see a possum running around in here, kill it. It's not a pet. - Jackie Moon

1. 
   polarchip | Apr 23, 2009 01:10am | #25

   hi Zolton,

   Commin in loud & clear....plenty of food for thought regarding wood grain orientation in plywood and the way jig saw blades are sharpened.  I really think you're on to something here,

   JJ

10. 
    davidbrum | Apr 22, 2009 09:02pm | #23

    If you have to make a bunch of circles, you might look into something like this. I haven't used one, but it sure looks like it would be easier and quicker.

    http://www.arcusblade.com/

    David B
1. 
   polarchip | Apr 23, 2009 01:06am | #24

   hi davidbrum,

   I'll be darn...never would've imagined that these were available!

   JJ

2. 
   Taigert | Apr 26, 2009 11:44am | #41

   All I can say is thats insane!

11. 
    USANigel | Apr 23, 2009 01:35am | #28

    Set your cut so the blade teeth are the leading edge and in line with the pivot. any binding and the blade will wonder.

    You had best use a router to clean up the edge because oak plywood "shatters" and will leave a rough edge as you cut across the grain.

    You don't need to spend lots on the router, you can get away with $50 but they do improve quickley with a few more bucks!

12. 
    robkress | Apr 23, 2009 05:01am | #29

    JJ,

    Skip the jig saw and go straight o router.

    Route with a 1/4" bit to start. Then when all the waste is gone, change the bit to a 5/16 or 3/8 and make one full cut, final pass.

    Clean up edge as you like.

    Rob

    
1. 
   polarchip | Apr 24, 2009 02:52am | #36

   hi robkress,

   Thanks for the picks.  Wow, I'm speachless....that solid hardwood is gonna be one terrific table top.  I'm curious though...how do your router bits handle cutting hardwood?  Do the bits get very hot? 

   Incidently, our one and only lumber/hardware dealer, have the same Makita router in stock only it's got a "D" handle.

   JJ 

1. 
   robkress | Apr 24, 2009 06:31am | #37

   JJ,I have the D-handle Makita base as well as the plunge. I prefer the D-handle to the double ball grabber style. Feels like I get better control.Really (I was brief in my first post), sometime there's no substitute for the right tool. If you don't have a router now, you should get one for this job. You'll then be saying "wow I can't believe I ever worked without it." The router bits do not get hot as far as I know. Perhaps they do but never really touch them. As I recall (it's been a while), the wind coming off of the gun blowing out the chips from that round were indeed hot. But that had no ill effect on the outcome of the big round.In general, I cut with an undersized router bit and then go to the proper size bit. That way all the flex of the router bit happens in the under size state and the final cuts at size are perfectly nominal dimension.The kind of router bits I use are actually end mills for metal machining. I get them locally in Cleveland but they can also be purchased at the following websitehttp://www1.mscdirect.comI typically use 4 flute, full carbide.Yes, the table was something to create. I really never had any idea how big a 6' round table top was and how hard it would be to manage (I built the room with the table only in my mind). The table is made out of European beech and in fact I paid the price for that. The pics are from the original cutting of the top. After I was finished, I move the top inside my house for finishing (basement). And when I got back to it 2 weeks later, the top had turned into a pringle potato chip. Oh the horror!!! I actually had to cut off 1/3, glue on new stock, and re cut the round. Total bs. Any way, that table (in my breakfast room) is where I sit every night doing work and hanging out at Knots. So here's a few more pics,Rob KressP.S. I have no idea how to remove files that are wrong. Sorry about the two goofy files

   
1. 
   polarchip | Apr 25, 2009 06:58am | #40

   hi robkress,

   You did a fantastic job on your table.  Thanks for posting picks,

   JJ

2. 
   JMartinsky | Apr 24, 2009 05:31pm | #38

   Dear Rob,
   Yep, that's how I do it. I LIKE the way that you mounted the router, creating a bevel.Best,John

1. 
   robkress | Apr 24, 2009 08:32pm | #39

   John,The legs have the same 10 degree cant on them so I figured I would match the edge of the top. Really not too tricky. Just a detail that I thought was important.Rob Kress

3. 
   mr_kramer | May 22, 2009 03:45pm | #42

   Hey, I like your set up. That's pretty nifty.

13. 
    WoodyAl | Apr 23, 2009 07:15am | #30

    Polarchip, this may be a dumb question and has nothing to do with your current problem but I'm curious. Are you working with 2) 4'x8' plywood sheets that are (or get) fastened together somehow? I'm just trying to imagine an 8' square sheet of plywood fitting in my shop and how I would get it home in my pickup.

    Sorry man, it's late, this screen is all blurry, the keyboard looks more like a roadmap and my mind is busy trying to figure out why it's not getting to rest.

    Goodnight.

    Al

1. 
   polarchip | Apr 24, 2009 01:40am | #34

   WoodyAl,

   The 3/4" oak plywood that I'm working with are approx 21" X 49" (the 8 X  4 sheets sold here in the great white north are approx 49" wide)   I'm building my own version of two popular & currently available direct/reflecting loudspeaker cabinets.  I've been doing most cuts with my circ saw, off hours at my day job mtce shop (we're allowed to do that) and the rest of the work which includes jigsaw cutting is done in my apartment kitchen.

   Regarding the drivers for my cabinets....the originals have 9 full range drivers and I'm guessing that each driver is 8 ohm and that they're connected in a series/parallel configuration.  My own version has four -- 3 way systems, each system having a woofer, a midrange and tweeter---also in a series/parallel config. except mine has a 3 way crossover network.  The drivers that I purchased is from a major loudspeaker dealership in the Kitchener/Waterloo area in Ontario, Canada....none of the drivers I purchased are top of the line though.  Although I haven't turned up the volume way loud,  they sound OK at low volume in my apartment.

   I used a good one side 3/4"plywood at first and purchased some oak veneer from LV but after reading the instructions, decided that it wood be better to replace the tops & bottoms of my cabinets with 3/4" oak plywood (installing veneer I figure might be bitting off way more then I can chew)  Furthermore, instead of having a 6 degree angle cuts as I had done with the GOS plywood, I decided to have the oak tops & bottoms with rounded front cuts (just like the originals that are currently sold)

   JJ

    

    

      

   Edited 4/23/2009 7:05 pm ET by polarchip

   Edited 4/23/2009 7:08 pm ET by polarchip

   Edited 4/23/2009 7:13 pm ET by polarchip

   Edited 4/23/2009 7:14 pm ET by polarchip

14. 
    489tad | Apr 23, 2009 03:06pm | #31

    I would cut larger with the jigsaw and finish with a router.  How are you supporting the 8' circle from flexing?  I would stack some blue board insulation on the floor and work off that?  That said I'm not sure flexing is a problem in your case.

1. 
   polarchip | Apr 24, 2009 02:00am | #35

   hi 489tad,

   The oak plywood I'm cutting is roughly 21" X 49".   On the floor, I've got a few books and plywood sits on the books.  One end of my circ cutter rig is screwed into plywood at midpoint (10.5") and the other end gets the cut.  Once one side is done, I turn my plywood piece 180 degrees, clamp a piece of wood at the end that I just cut (in center..ie 10.5") screw in circle cutter rig and proceed with cut.  And so, each end of my 21" X 49" plywood has a radius of 4 foot.  Ultimately, after the 4 additional straight cuts with circ saw are done, this gets me one top and one bottom for one of my loudspeaker cabinets. 

   I repeat the above with another 21" X 49" piece for the other loudspeaker cabinet.

   JJ

   Edited 4/23/2009 7:57 pm ET by polarchip

15. 
    MikeIke | Apr 23, 2009 07:35pm | #32

    Good morning! Just last week I was cutting curves on a porch rail in 2x 12 with my Bosch Jigsaw. I found that the medium orbital setting with a moderate (Say 50% squeeze on the trigger) power setting kept my blade running pretty straight. I was careful to really really take my time on cutting speed, as well. I tended to push too hard, and sure enough the blade would start flexing on me. I was using Bosch Progressive blades, 10 TPI. A small amount of cleanup with either spokeshave or plane was enough to get it looking pretty good!

1. 
   polarchip | Apr 24, 2009 01:12am | #33

   hi Mikelke,

   Regarding "pushing a little too hard causes the blade to flex".....thanks very much for that info and furthermore, ironically, the "Master Mechanic" blades that have performed better then the others for my rig also had 10 TPI !

   JJ