Problem cutting blanks

[DAL1957]

I'm having a few issues with cutting round blanks for turning with my band saw on my blank cutting jig.

The initial plunge cut goes fine, but then a while after starting the curve (worse with larger pieces) the blade deviates to the right, and once it has deviated there is no fixing the problem, if I back out and come in again the blade just follows the original cut. And once the blade has deviated the saw starts to bog down and almost stall if I persist.

You can see what has happened to my jig with the blade bending.

If the piece is not too big the deviation can still happen with the blade cutting in a little too deep and at the end of my circle it has deviated by 5-10mm giving me a not quite round blank. You can see the result in the second picture with the step in the circle.

The blade is tensioned as per the manual with the knob on the back set for the width of the blade. Do I need more tension?

Band saw is a Powermatic 14 with the 12" riser block fitted.





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[Nubsnstubs]

I'm only being funny with my next statement. You oughta be happy with that...


I only said that because what of happens when I use my jig, I get the same kind of cut as you did, but it also cuts a curve on the sides of the blank, plus it stalls a lot. It's a Rikon 14" with the tension guide. When I use it I can never cut a good round. From what I've seen and read, the point of your center pin should be in alignment with the front of the teeth, or maybe it's the gullets on the blade. I've tried it both ways, and still can't get a clean cut.

One thing I've done is to make sure the teeth are on the center line on the top wheel and keep my guide bearings at the gullet line.

My old bandsaw, a Duro 14" with a 9" height capacity is so much easier without having a tension indicator. ................... Jerry (in Tucson)USA

[Richard Hodsdon]

Why is that a problem. You are going to put it on a lathe and have to true it up anyway. If you are storing it and drying it before turning it is going to become oval due to the difference in longitudinal and radial shrinkage (or is it tangential) and so will be out of round when yo mount it on the lathe.

[doug3030]

I'm having a few issues with cutting round blanks for turning with my band saw on my blank cutting jig.

The initial plunge cut goes fine, but then a while after starting the curve (worse with larger pieces) the blade deviates to the right, and once it has deviated there is no fixing the problem, if I back out and come in again the blade just follows the original cut. And once the blade has deviated the saw starts to bog down and almost stall if I persist.

The answer to almost every bandsaw problem ever is in this video. However, you have to do everything in the video. It's a system. You can't do just part of it and expect good results. If you have the right blade and it is sharp enough and the bandsaw itself is up to the task then it is a matter of setup and the video explains it as well as anyone I have ever heard.

YouTube (https://www.youtube.com/watch?v=wGbZqWac0jU)

[Mobyturns]

The answer to almost every bandsaw problem ever is in this video. However, you have to do everything in the video. It's a system. You can't do just part of it and expect good results. If you have the right blade and it is sharp enough and the bandsaw itself is up to the task then it is a matter of setup and the video explains it as well as anyone I have ever heard.

YouTube (https://www.youtube.com/watch?v=wGbZqWac0jU)

Like any cutting machine, the bandsaw must be setup well and maintained to keep the setup. Bandsaws are also more prone to misalignment issues from general wear & tear and abuse as many things affect the final desired outcome. Most issues stem from #1 poor blade selection; #2 a dull bandsaw blade; #3 incorrect tension, #4 poor setup - tracking etc.

Even blade choice, tpi, steel band thickness, width, teeth set, sharpness all affect the bands ability to remove the waste from the kerf, and its ability to maintain stiffness and track accurately without drift or bowing.

When cutting circles the teeth on the outside of the band cop more wear and tend to loose their set much faster than the opposing teeth which accounts for some of the issues. As the cut progresses, in your example above, it changes from crosscutting to ripping, crosscutting, ripping then finally ending as a crosscut. Your blade choice, tension setup, feed rate, blade tracking all determine how well the cut is performed in those changing grain orientations.

You have a relatively fine tpi blade which will struggle to remove waste in that depth of blank, so a much coarser tpi count may solve some of your issues. A slower feed rate may help. Using the OEM blade tension settings is a very rough guide at best.

Watch Alex Snodgrass' video and follow his tips and you should be well on your way to sorting most issues.

[orraloon]

As has been said to cut out circles in really thick stock everything has to be set up just right. The tension gauge can not be relied on and after fitting a riser it will be way off. Blades dont last long doing that either.
The good news is the blanks really dont need to be round in any case. I just knock off the corners to get an 8 sided blank. I find thats usually good enough but if you like then knock off the corners again and it's almost round. In my early days of turning it dawned on me that a good roughing gouge will outlast $#!7load of bandsaw blades.
Regards
John

[China]

As said above there is no need to cut a blank perfectly round, I have turned at least 2,000+ items that ended up round on my lathe/s over the years, and I can't remember ever bothering to cut a blank round.

[Skew ChiDAMN!!]

LWhen cutting circles the teeth on the outside of the band cop more wear and tend to loose their set much faster than the opposing teeth which accounts for some of the issues. As the cut progresses, in your example above, it changes from crosscutting to ripping, crosscutting, ripping then finally ending as a crosscut. Your blade choice, tension setup, feed rate, blade tracking all determine how well the cut is performed in those changing grain orientations.

This. Have you tried cutting a thin platter blank lately? If so, does that deviate as much?

If not, then it's likely to be the thickness of your blank exacerbating the effects of changes in grain pattern. That's really fiddly to deal with... and I don't think it worth the effort myself. :shrug:

If it is pretty much the same, then the teeth on one side of your blade are blunter than those on t'other. This is usually caused by either cutting an inclusion (including nails, small grit and stones, etc) in the wood OR by cutting curves in the same direction all the time.

If I'm cutting a lot of rounds, I like to alternate my jig from side to side of the BS table (assuming I have room) simply for that reason. Although, being inherently lazy, I'll sometimes do 3 or 4 cuts one way before I swap over... ;)

[DAL1957]

Why is that a problem. You are going to put it on a lathe and have to true it up anyway. If you are storing it and drying it before turning it is going to become oval due to the difference in longitudinal and radial shrinkage (or is it tangential) and so will be out of round when yo mount it on the lathe.


The starting pieces can be really quite large and very not round, would probably keep me hacking away with the roughing gouge for days, and on a slow speed.

I've included a few photos of the pieces I am working on right now. You can see they are probably just a little big to go directly into the lathe, at least for me. These are the pieces that have been giving me significant grief in the band saw.

The second picture shows the ones I have just done, and awaiting labeling and storing. The 3 right-most ones all show the stepped cut from the blade leaning in. It certainly isn't an issue when they hit the lathe as they will round up quickly, it's that on the larger pieces the blade bogs right down and almost stalls the saw.

The final pic shows my slightly OCD system of cutting & storing a years supply of blanks.



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[DAL1957]

And thanks all for you inputs and words of wisdom.

Sounds like a band saw tune up might be a very useful way to spend a few hours. I'll download the video later and pop it onto the iPad and take it out to the shed.

And I guess the other option of just knocking of the edges until it's closer to round than square would probably work fine as well, that's why they invented roughing gouges. I suppose a little early work with a chainsaw might also be beneficial.

[Colin62]

Am I misunderstanding what’s meant when I read people talking about roughing gouges and bowls? Every time I see that I worry that someone might be using a spindle roughing gouge on a bowl, and I’m not a big fan of that at all.

[DAL1957]

Am I misunderstanding what’s meant when I read people talking about roughing gouges and bowls? Every time I see that I worry that someone might be using a spindle roughing gouge on a bowl, and I’m not a big fan of that at all.

Got me slightly with the terminology, I am not actually sure what a "Spindle Roughing Gouge" is v's a "Roughing Gouge". What I call a Roughing Gouge is the big one that you initially use to take the rough edges of the outside, and generally get a rough/out of round piece of wood to fairly near round before then moving to either a spindle gouge or bowl gouge (my favourite chisel) to start the finer shaping.

But yes, I have seen numerous warnings about NOT trying to hollow a bowl with a "Roughing Gouge" as it can be quite dangerous.

[Colin62]

I’m pretty sure that they’re the same thing. Sometimes the word “spindle” is put in front to emphasise that they’re designed for spindle turning, and not bowls. I just use a bowl gouge for turning odd shaped lumps into round lumps. I’m not even sure how I’d approach using a roughing gouge and I suspect that it wouldn’t save much time (if any) over a nice big bowl gouge.

[Guy28]

Hi,
I think that the issue here is not one of bandsaw drift (although it doesn't help). I found the same issue with a similar jig and was advised that the problem was that the pivot point was not in perfect alignment with the cutting edge of the blade. Once I had the blade and the centre spindle aligned - everything worked fine. if the pivot point is in front or behind the cutting edge, you are no longer cutting a perfect circle and this is what causes the cut to move and bind the blade.
Cheers,

[NeilS]

All good advice above on setting up your bandsaw to cut a true circle.

However, I gave up on bothering to do round blanks a long time ago.

I straight cut small blanks on six sides.

I straight cut larger blanks on 12 sides (six sides then trim off the apexes).

Much faster than trying to get a round blank and once on the lathe they become round in seconds.

As I'm not trying to cut curves I use a 1-1/4" wide blade with 1.3 teeth per inch (bi-metal from Henry Brothers). It gives a rough cut but goes quickly through anything I throw at it.