Small power hacksaw, how fast should it cut?

[WobblyHand]

Have an unknown brand small power hacksaw that only can take a 10" blade. I have a 14 TPI blade in it. The blade isn't new, but it feels pretty sharp. I'm cutting a piece of 1.625" x 3.75" 7075. It's taking what I consider to be a long time. It's been 4 hours and 20 minutes so far and it's maybe 50% through. I have heard they are not the speediest of cutters, but, I'm surprised. Perhaps the saw has been set up totally wrong. Or this saw just is not good.

Which way do these saws generally cut? On the push or pull? On this saw there seems to be an adjustment with a spring loaded detent. I have the lever all the way to the rear which seems to cut the fastest. By that I mean I see more aluminum chips coming out. There's no name plate on the saw, although there is a place for one, it seems to have been removed. There is a number on the frame on the casting. I can get a picture of it. (Yeah, pics or it didn't happen!)

Are my expectations too high for this saw? I've been eeking this saw along. It really need a rebuild and new gaskets for the gearbox.

 

[projectnut]

Most smaller power hacksaws cut at between 100 and 140 strokes per minute when pulling back toward the crank pivot. The rule of thumb is no less than 3 teeth should be in contact with the part and no more than 24. Less than 3 teeth in contact is likely to strip a tooth off the blade. If you have more than 24 teeth in contact the gullets are likely to load and either prevent the blade from cutting or cause it to jam in the kerf and break it.

 

[Ulma Doctor]

Hacksaws should be cutting on the forward stroke, the blade should lift slightly at the end of the stroke to keep the teeth from dragging on the rear stroke.
For aluminum, I would use a low tpi (6 to 10) kerosene, diesel fuel, cutting wax or other cutting agents would prevent chip welding

7075 is tough stuff, I would expect longer cutting times- but 4 hrs seems excessive

 

[WobblyHand]

Most smaller power hacksaws cut at between 100 and 140 strokes per minute when pulling back toward the crank pivot. The rule of thumb is no less than 3 teeth should be in contact with the part and no more than 24. Less than 3 teeth in contact is likely to strip a tooth off the blade. If you have more than 24 teeth in contact the gullets are likely to load and either prevent the blade from cutting or cause it to jam in the kerf and break it.

From your explanation, the cut is on the pull. I have tried both ways, in the past, but one doesn't seem faster than the other. I will make sure the teeth cut on the pull. For a hand hacksaw the cut is on the push. This is a bit confusing.

It would seem that cutting a piece on the 3.75" face is not optimal. The built-in vise only can clamp to 3", so it is grasping the 1.625" part, that's the best I can do.

The saw is still cutting, but it's been running for 5 hours! I could have cut the piece by hand a lot faster. Of course the power hacksaw cuts straighter than I can.

 

[WobblyHand]

Hacksaws should be cutting on the forward stroke, the blade should lift slightly at the end of the stroke to keep the teeth from dragging on the rear stroke.
For aluminum, I would use a low tpi (6 to 10) kerosene, diesel fuel, cutting wax or other cutting agents would prevent chip welding

7075 is tough stuff, I would expect longer cutting times- but 4 hrs seems excessive

Coarsest TPI I've been able to find in a 10" blade is 14. There seems to be a lot more TPI's available in 12" blades. Of course, maybe I'm looking in all the wrong places!

Hand hacksaws are setup to cut on forward stroke. Are power hacksaws configured the same way?

So far I don't see evidence of chip welding on the blade - it's going too slow to chip weld! It's been 5 hours now. Might be another hour. Seriously, 6 hours to cut 1-5/8" x 3-3/4" aluminum, that's just too, too long. I need to reduce that time, by a lot.

 

[markba633csi]

Sounds like the saw was made for light duty use, since it only accommodates a 10" blade. There may be something wrong or out of adjustment though
AFAIK most power hacksaws cut on the pull stroke; some have a feed mechanism with adjustable cutting pressure and some just rely on gravity
-Mark
A bandsaw would likely cut that piece in less than 10 minutes.
How many strokes per minute is your saw making?

 

[Aaron_W]

That is a very small power hacksaw. I have a Covel (same as the common Craftsman) and it uses a 12" blade. That saw is rated as 4x4 so you may just be beyond the capability of the saw. Not just a matter of what fits but also the geometry of the blade when cutting.

I've had my 4x6 bandsaw stall out cutting a piece of steel close to max capacity. It cuts fine to a point but will eventually just start floating, there is so much blade in contact that it no longer is putting enough weight on the blade to get a good bite. Using one finger to push down lightly on the end will usually help it to get past that stall point, but the better solution that I have adopted is I now have a bigger 6x10 bandsaw to cut the bigger stuff.

4 hours there is either something wrong with the saw or you are just beyond its capacity. Like you said you could have cut it by hand by now.

 

[WobblyHand]

Finally done. Started cutting before 3:15pm. Finished at 10pm.
This saw forgot to eat it's Wheaties. Need to find something better.

 

[iancdodds]

Have an unknown brand small power hacksaw that only can take a 10" blade. I have a 14 TPI blade in it. The blade isn't new, but it feels pretty sharp. I'm cutting a piece of 1.625" x 3.75" 7075. It's taking what I consider to be a long time. It's been 4 hours and 20 minutes so far and it's maybe 50% through. I have heard they are not the speediest of cutters, but, I'm surprised. Perhaps the saw has been set up totally wrong. Or this saw just is not good.

Which way do these saws generally cut? On the push or pull? On this saw there seems to be an adjustment with a spring loaded detent. I have the lever all the way to the rear which seems to cut the fastest. By that I mean I see more aluminum chips coming out. There's no name plate on the saw, although there is a place for one, it seems to have been removed. There is a number on the frame on the casting. I can get a picture of it. (Yeah, pics or it didn't happen!)

Are my expectations too high for this saw? I've been eeking this saw along. It really need a rebuild and new gaskets for the gearbox.

Are you sure the the blade carriage is not hung up on another part of the saw, somewhere. I suggest looking as I fell foul of a similar thing with my bandsaw. In my case the carriage was snagging the vice


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[Lo-Fi]

My Wellsaw would do that in about 20 minutes with a 14tpi blade. Is there enough weight on the blade and is the motor turning the right direction? Usually they cut on the out stroke, with the drive being arranged such that the levering caused by the crank pushes the blade into the work on the forward stroke. On mine, the direction the crank turns is critical to proper functioning.