T.P.I.

Hi all

I am in the process of restoring a powered hacksaw, and now need to order a 35 cm blade for it. I will be mainly cutting large pieces of aluminium and brass , with only the occasional piece of steel. Would a 10 tpi blade be suitable.

Cheers Mike

10 TPI will be just what you need. I only keep 10 and 14 TPI blades and always cope.

TPI should be based on the thickness of metal being cut, the minimum should be three teeth in contact. When cutting say 3mm 25x25 angle (RSA), it should be put in the saw so that the corner is uppermost. This spreads the contact area for the saw teeth so your teeth are lying over a litttle more than 6mm.

Thanks for replies. I will order a 10 tpi blade then.

Cheers Mike

Rule of thumb: at least 3 teeth in contact with the work.

I was thinking about the rule of thumb - 3 teeth is presumably to limit the depth of cut - so you don't end up trying to take a full tooth gullet depth cut in a thin material - thus bending the fragile edge rather than cutting it, or creating a load on the saw that is too high to push through the material.

I think this certainly applies for human powered saws - no doubt many of us have at some point tried to use a too course blade in a hacksaw (or in my case more often a jewellers saw).

My power hacksaw however has a defined depth of cut setting - the blade is fed down by a certain amount on each stroke. I rarely alter the feed setting - but then Im usually cutting the same sort or big chunks of stock.

Point is that if the hacksaw has a feed setting ( and not just a gravity weight) you can probably successfully use a courser blade than might be suggested otherwise.

Thoughts?

Dave

3 teeth is presumably to limit the depth of cut

Noo. The three teeth rule is to be sure that the saw cuts in a straight line on all those teeth and the cut depth is consistent and controlled. The tpi should not be excessive for the material and width of cut.

This rule applies to all saws - machine or handraulic. This is one reason why cutting thick bars with a 24tpi hacksaw is difficult/inefficient - the gullets simply become fully filled before the teeth exit the cut, thereby restraining the cutting action, across that part which is beyond where the gullets become congested with swarf.

How is limit the depth of cut different to cut depth is consistent and controlled?

Finer toothed - yes the gullet is smaller and fills, but courser toothed the gullet is potentially deeper than the material thickness - so if you can control the DOC such that you don't take too deep a cut what disadvantage does it bring?

In extremity a shaper is a power hacksaw with a single toothed blade (especially if you squint a bit )

Hand saws are poorly guided in comparison to machine saws.

Dave

Hand saws are poorly guided in comparison to machine saws.

If you want to try being picky, go and have a look at videos by Allen Millyard. His, most certainly, are not. In fact far better than s lot of bandsaws out there!

A skilful bloke with plenty of practice time in.
Not sure how that’s relevant to machine hacksaws or controlled depth of cut tho?