Abrasive chop saw - cutting to size question

[Wany]

I will preface this question by stating I am an inexperienced hobbyist wanting to learn. I work in IT and it's 30 years since I did my CDT Technology GCSE.

I've bought a second hand Sealey 355mm abrasive chop saw. I have been cutting 25mm box section steel on a 45 degree angle to make a welding cart. I have drawn up some plans so I know what length I need each side to be.

To ensure the frames are square I need to ensure that each of the opposite sides are of the same length and to be a better engineer I need to try and make my work match my plans.

I have made one frame but the issue I had was that despite cutting the first mitre, measuring up, marking my next cut and lining that up to a static blade edge each piece was not the same length by a couple of mm.

My question is am I missing a trick in how I am lining the work up to cut or should I be cutting my work slightly longer and grinding the two pieces to be the same/correct size? The saw table doesn't have any markings to work to. Any advice would be gratefully received.

 

[Maker]

How are you marking it out? Some layout dye (Or a sharpie) and a scribe line will be more accurate than a felt pen/chalk marker/etc, lay it out carefully and cut it just leaving the line on the work, you should be able to get it spot on straight off the saw.

 

[Shedendman]

Are you cutting on your line or by the line,taking into account the thickness of the cutter itself
Me,i over cut,ie slightly longer as you suggested,yep,better to file/grind a bit back that coming up too short
Cut one piece to what length/angle etc you need thats spot on,use that bit as a template for further cuts

 

[jimbo84]

I have a Metabo one of these and do find the blade will wonder a little, particularly on a new blade that is much larger, there is quite a bit of flex in a 235mm blade.

To help I contact the blade with the material as gently and possible initially and let the blade do the work, don't force it otherwise it won't cut straight. Mine has a gauge on the vice but I use a set square to square it up to the blade and a protractor for the 45 degrees. I find 45s are often out though. It's just the nature of the machine.

 

[Paul.]

I cut all my stainless box and angle with a Ryobi chopsaw, disks can wobble a bit when new, buy good ones, mark a scribe line for the cut then line it up and blip the trigger to spin the disk and see if its running true, when cutting mitres don't use the adjustable vice, leave it set square and make a mitre fence, hold the job to the fence with a G clamp don't use the vice, you'll push the back jaw out of position,
with a bit of care you can make very accurate cuts, have a look at this post of mine to see what can be achieved, it also shows my mitre fence.

https://www.mig-welding.co.uk/forum/threads/a-few-random-stainless-jobs.54058/page-4#post-829968

https://www.mig-welding.co.uk/forum/threads/pump-storage-trolley.55473/

 

[hotponyshoes]

I use the template way as mentioned above.
If the parts need to be the same but the actual dimensions are not critical then cut the first part and lay it on top of the next part to be cut. Align the end you are not cutting, clamp together then you can slide the uncut length into the saw, pull the blade down until it is almost touching the uncut piece and push the cut bit up against the blade. Tighten the vice and cut.

For something with a more on only one end you can make one 45deg cut in the centre of a bit of tube, lay them onto of each other then cut both of the other ends at the same time.

For a lot of stuff for frame work and such depending on the capacity of the saw you can cut most of the lengths in pairs providing you can clamp them the right way in the vice so they are pressed together ie. you don't want them stacked on top of each other if the vice grips from the side.

Another way to work with chop saws is mark and make a tiny starting cut, just enough to get the full width of the blade cutting.
You can then hold the parts together and check all the notches line up. If not you can rotate the part and try again. If they do then the notch acts as a easy way to line up and cut through. Bit time consuming but does help on the cheaper saws or ones that have a bit of play in them.
Sometimes on abrasive saws it helps to get a full width cut going then lift the saw back up. Start to cut again and watch to make sure the blade is going into the same slot as before.
On angles especially the blade can push the metal away as some of the voices can seem to clamp firmly yet still have some sideways deflection in them when tight.
Extra clamp holding the stock to the saw frame will work once you have worked out which way stuff moves in your particular saw. You can work that out by marking a test line then mark a couple more at say 5mm either side. Cut on the marked centre line then measure from the cut to the 2 marked lines and work out where it is going wrong

 

[wyn]

As others have said, those chopsaw blades can flex, especially if you're cutting 45*

 

[pedrobedro]

I have used mine for years and have built quite a few things including a couple of car chassis and can achieve a reasonable degree of accuracy. One method is to cut your tube to length then put the mitre on after

 

[8ob]

If I am building square frames with box I always stack the tube in the vice and cut sides in pairs, its that or fettle and I don't do fettle

Bob

 

[eLuSiVeMiTe]

If I am building square frames with box I always stack the tube in the vice and cut sides in pairs, its that or fettle and I don't do fettle

Bob

My method too.
Also a stop to position is helpful

 

[Wany]

Thank you all for your support and advice. I have some things to try when i make the next frame along with ideas for new/additional tooling.

 

[Munkul]

I think some abrasive chop saws are just simply more rigid/accurate than others.

ancient makita chop saw at home - quite good, even on mitres.

brand new milwaukee at work - so, so bad it's amost unusable. even straight cuts the blade deflects by at least 2mm, more if you force it. And forget about mitres!

As said, good quality blades make a difference. But for me it's all about cold cut TCT now