Bandsaw cutting radius

[transatlantic]

I have some curves I need to cut that have about a 1" radius. I had a look at the following guide and so ordered some 3/8" blades from tuffsaw :

3/8" - SuperTuff Carbon 6 TPI
3/8" - SuperTuff Carbon 10 TPI
1/4" - SuperTuff Carbon 6 TPI

I setup the 3/8" 6 TPI blade and am having trouble even making the 1.5" radius. When I make the turn, I can see the blade being fairly twisted, and I hear rubbing of some sort coming from the the upper wheel casing (BS300).

I then tried the 1/4 inch and that appears to work fine for 1.5", but it kinda does the same thing for the 5/8" radius.

It just feels like that the radius according to that guide is far too tight for the blade they recommened? Should I be able to see the blade visibly twist between the upper and lower guide? .. and of course the rubbing sound in the upper wheel compartment can't be right?

 

[twodoctors]

I have a similar problem.

Using my Axminster 1/4" 10TPI I also have to twist the blade quite a lot to make any turn. So much so that I am in constant fear of the blade snapping during the process. 10TPI is too weak in my bandsaw anyway and it's burning rather than cutting its way through. I'll post a picture of my effort later but 3/16" seems to be the way forward. Having said that my blade broke on second use without aggressive turns. Probably just unlucky.

Good luck.

Adrian

 

[sunnybob]

The blades do twist and they do make noises as they rub against the guides.
One thing I have learnt the hard way is that you need to keep going. You can get bogged down watching the blade, which makes you slow the wood, which causes the burning.

I've done some extremely small diameter circles, less than half inch across in 3/4" soft wood using a 1/4" blade, but that blade didnt like me while i was doing it.
Be bold, let it know who's boss.

 

[custard]

Those radius guides are very approximate. If your blade has a lot of set on the teeth you can go much tighter than those figures suggest, but if there's less set then you can't achieve those figures. I mainly use an M42 1/2" blade and it has generous set, I pay a price with a wider kerf but then get the benefit of quicker curves. You pays your money and takes your choice!

 

[Neil S]

I can cut tighter curves with the 3/8" blade supplied with my bs300e than the 1/4" blade I bought from tuff saws. The 1/4" blade just twists and burns. I'm thinking it's because the guide discs are too loose and cannot stop the blade from twisting. If I tighten up the guides any more they just Jam at the back of the blade. The wider blades sit deeper into the guides so the guides cannot wobble as easily.
To confirm this I plan to try some wooden dowel instead of guides that I can place right up to the blade. This might then support the whole blade width and stop it from twisting.

-Neil

Sent from my GT-I9505 using Tapatalk

 

[nev]

In case its relevant and you haven't seen my recent post in TwoDoctors thread... same blade as you're using there, I easily manage about 1/2" radius* cut...
snapped-tuff-saw-blade-t104706.html

* I think 1\2' radius = 1" diameter innit?

 

[Paddy Roxburgh]

You probably already all know/do this, but just in case not....where possible make relief cuts on all tight radius cuts.This is obviously ony possible when the convex side is the keeper and the concave the waste.
Paddy

 

[CHJ]

Because I only cut for turnings etc. and do not need a thin kerf I always order blades with the maximum kerf available.
These certainly would be no use for Bandsaw boxes but do enable a radius cut far tighter than the 'recommended' without any sign of binding.

Personally I would not be happy with any sign of the blade twisting whilst riding in the kerf, are you taking a close note of where the pivot point of your curve is in relation to the front of the blade.

Sorry if this a case of 'teaching to suck eggs' but:-

If you are cutting a full circle the pivot point needs to be in line and at 90deg. to the blade leading edge, if it's not then the blade will endeavour to cut a spiral curve ether over or under desired radius.

This will apply even to a part curve segment so radius pivot point needs to be adjusted as you cut to remove this 'drifting' trait which may show as a twisting of the blade in the first instance.

 

[transatlantic]

Because I only cut for turnings etc. and do not need a thin kerf I always order blades with the maximum kerf available.
These certainly would be no use for Bandsaw boxes but do enable a radius cut far tighter than the 'recommended' without any sign of binding.

Personally I would not be happy with any sign of the blade twisting whilst riding in the kerf, are you taking a close note of where the pivot point of your curve is in relation to the front of the blade.

Sorry if this a case of 'teaching to suck eggs' but:-

If you are cutting a full circle the pivot point needs to be in line and at 90deg. to the blade leading edge, if it's not then the blade will endeavour to cut a spiral curve ether over or under desired radius.

This will apply even to a part curve segment so radius pivot point needs to be adjusted as you cut to remove this 'drifting' trait which may show as a twisting of the blade in the first instance.

Thanks for the advice. I generally just follow the line, as it's quite difficult to envision the pivot point as it would be constantly changing for say an S curve, but I will definately keep that in mind when cutting more circular stuff!

 

[CHJ]

... I generally just follow the line, as it's quite difficult to envision the pivot point as it would be constantly changing for say an S curve, ....

That's the whole point, if you don't move the angle of attack of the wood as you work then you will twist the blade or it will be trying to go off track all the time.


For an extreme example of moving the work piece to presented the direction of cut to the front of the blade watch a scroller manipulating their work.

 

[sunnybob]

Its also like driving a very long car, you have to start turning before you reach the corner.
And if its a sharp corner, the analogy is closer to driving a rear steering truck. Have you watched a fork lift go from lock to lock while only moving forwards a couple inches? Plan ahead with the cut.