Cutting the angle iron down with grinder and abrasive disk

[Alan_c]

I have been working on the design of my angle iron trimming machine and decided to make a wooden prototype to test the concept. It is a combination of Geralds original idea and a sample on J.R.'s thread.

I felt it would be difficult to move a 3m (10ft) length of angle iron past a fixed grinder and still keep it under control. My moving grinder attachment rides on alwayse (http://www.alwayse.co.uk) ball units (a steel ball riding on many smaller balls held captive in a cup). I had originally thought of using normal bearings on edge but was concerned with the tendency that they would have of moving off line if not travelling 100% parallel to the angle iron. With these ball units I will be able to apply side pressure as well as longitudinal pressure.

The prototype was made of some ply I had laying around in the garage so excuse the odd bit of paint and pen marks - I will be making a production model with steel as the ply has too much flex.

I am using a Ryobi angle grinder as its what I had available but then it comes with a hidden advantage. The gear head has metal threaded bushings that were originally used to mount the guard, this makes it easy to mount to the holding plate. It has three M4 threads and one M5 thread. I have used SS cap screws to mount the holding plate.

The four set bolts allow me to adjust the height of the cutting disk off the table as well as allowing me move it higher to mount a grinding disk to polish the top of the cut angle iron.

I dont like that bit of cutting disk exposed at the back so the production model will have a modified holding plate to cover the disk.

I did not have a sample piece of angle iron at hand so I have shown the assembled unit next to a length of timber instead.

[J.R. Hatcher]

Don't try to cut deep, I found this out the hard way. The cut will heat up and the 1/16" disc will suffer loss. The first 12' rail I cut down took about 4 disc, the second took almost as many. When I started the 8' rails I worked smarter by taking longer faster passes. The 8' rails took 1 disc each and a lot less time. Go easy when the disc cuts through, this is another place where you use up a lot of disc.

[Gerald D]

Yes, you don't use a grinder like a table saw. A grinder touching red-hot metal just chews up the disk. Use an oscillating motion that moves the disk to cold metal all the time. (Those chop-saw cut-off grinders are terrible at chewing up disks)

[Doug_Ford]

Beautiful craftsmanship Alan. I like the idea of moving the tool rather than the angle iron. I moved the iron and it was a real bear. I started out cutting the 8 foot pieces in case I screwed one up it would be cheaper to replace it. When I started cutting the 12 footers, I switched to a new silicon spray and it ended up creating a gooey mess that actually made it harder to push the steel. I didn't figure that out until I had cut for a couple of hours. I just assumed the 12 foot lengths were much heavier than the 8 foot lengths.

[Alan_c]

I made some mods to the grinder skate to fit my Ryobi grinder but it has ended up putting the grinding wheel in a different position to the standard item, this means I have to drop lower to the angle to get the full grind. I may just extend the slots so that the grinder holding plate is able to move further across. ( this means I will also have to extend the cut out in the base plate as the grinding wheel will foul the edge)

1631

[smreish]

Nice rail cutting tool...I sure bet it glides nice.

[Alan_c]

That rail cutting tool does move sweetly, I have just closed the holes in the top of the ball bearing units to stop the grinding dust getting in there.

[Alan_c]

Started cutting the Y axis angle iron for the rail - the cutting jig works great but seems to use disks at a rapid rate, went through 3 1/2 disks to cut just one rail, and no I wasn't pushing too hard. When the disk is new, it cuts with a good flow of sparks, but once past halway, the sparks get less and the disk wears at a much higher rate. I was using the thin (1mm) disks from both Norton and Klingspor. The Norton ones wore down much faster.

As I didn't have any more disks on hand and the closest supplier is over the Mountain, I decided to call it a day and join the Kids in the pool (temps over 30 deg C today, but predicting thunderstorms for tomorrow) :D:D

[Gerald D]

The good cutting disks are by Pferd - ask them for the thin Inox (Stainless Steel) disks.

[Alan_c]

Pferd disks rule, cut the second Y rail tonight with only one disk and it stayed cutting all the way down to the centre. Will do the bevels tomorrow.

[skypoke]

Belay all that...we got it done. As others have said, the selection of grinding discs is of paramount importance. I ended up ordering the Pferd discs. We used a fixed grinder arrangement to cut down and ended up milling on the table saw. Lots of fantasies during the process of a Mechmate carrying a grinder and making rails!

Chuck

[Kobus_Joubert]

Cut the Y-Rails down using the top part of the skate. Used about 5x Pferd 1mm thick disks to do the job.

1616

[Gerald D]

Kobus, how long did it take you to cut all the rails down?

[Kobus_Joubert]

Cutting the rails was one of those jobs that I thought would be a pain. So much that I got a quote from the company that did my laser cutting. Luckily for me he came with a mad price (almost the same as all the Mamba parts) and I had to supply my own steel this time. This forced me to do it myself. And what a piece of cake. Firstly I thought of using my table saw with a cutting disk. Did a short piece of rail, but this was hectic and too dangerous to my liking. I eventually clamped the angle iron onto my table saw top and grinded piece by piece using the table saw as a nice straight reference surface. All in all it took no more than one hour to do one rail. Much easier moving a small grinder than a BIG LUMPY piece of steel.

1618

1619

[lunaj76]

We ordered 2.5X1.5X.25 angle for the rails instead of the recommended 2.5X2.5X.25. Reason: only 1.725 of working height between bottom of grind head top plate and work surface (grinder is Bosch 1710). By using 2.5X1.5X.25 you get more life out of the cut wheel because the uncut rail will completely slide under the bottom of the grind head top plate. Am I making any sense? We used the pferd cut wheels and only used a few wheels cutting 40' of rail to height.

Justin

[Johannescnc]

This post moved from http://www.mechmate.com/forums/showthread.php?t=810 (http://www.mechmate.com/forums/showthread.php?t=810)

I have been following this thread for a while and wonder what the life expectation is from the rails to warrant the purchase of tools like these for one machine build... :confused: When I buy a tool I either buy a cheap one for short term use or a good one that I will use often. But, I have not had the fun of cutting down 40-50 feet of 1/4" steel yet either...:p So I would welcome the thoughts on this method or using a disc grinder... John

http://i221.photobucket.com/albums/dd69/johyn_foto/3802.jpg

I like the look of this.... inexpensive use of a common tool...

[Gerald D]

I will try and assemble some reports of folk who used this method into this thread. Please tell me where there are relevant posts in personal (or other) threads that I can copy to this one.

[Gerald D]

For the guys experienced in moving the grinder against the static rail (which I feel is superior to my "trash can" test), what are your thoughts on turning the rail around, to reference the grinder on top of the long leg of the angle iron? Realise that is a narrow face, and that clamping will be in the way, but I believe it will be easier to get a consistent rail height. . . . . .

[Kobus_Joubert]

Could be an idea to go that way. Even on my FLAT table saw surface and the angle clamped with 2 big G-Clamps or is it C- clamps, I still noticed a small variation...1-2 mm over the total length...maybe my bolts wore down quicker than anticipated?

[Gerald D]

With the way that Kobus and Alan clamped the rail down, a bit of dirt between the rail and table would make the grinder cut too low. Also, the angle iron bows when that edge is cut off - it might be bowing away from the table.

[Alan_c]

I drilled my rails first, then cleaned it all up before screwing it to the MDF support board (checked to make sure all was very clean) My variation over the length as measured with a digital vernier was no more than 0.2mm - more than acceptable I think for a "garage" process. I did not notice any bow, but if it had the mdf running surface would have bowed with it.
Also by running on the support (support flush with bottom of rail) ensures that should one run over some dirt or grinding dust build up or lift the skate slightly, the result would be a rail that is slightly oversize - i.e. easy to still bring it down to the correct size. If one runs the "skate" on an upside down rail and there is loss of contact will the running surface, the result would be a rail that is lower than required - i.e. can't be fixed without grinding the entire length down to that height.

[Gerald D]

I don't mean upside-down, I mean with the long leg pointing towards the grinder instead of away.

[hennie]

This will be my attempt at cutting the rails to the required hight.
With luck the hight of the disk was exactly what is specified.
The length of the sliding table of the saw will allow me to cut the rails a little longer than what is required so I will have some steel left for grinding the angles.
I can move the guide on the right to adjust the cutting depth of the disk.
I will make mdf blocks to tighten the angle iron on the sliding table by using the slots in the table.
(only had this little bracket to pass the idea as I have not cut the angle iron to size.planning to do it next weekend.)Will post pic`s as I do the cutting.

[Alan_c]

Nice idea Hennie...but, remember that the cutting process produces a large amount of fine steel dust and it would be a sin to gum up all the precision moving parts of that (what looks like a quality Felder) panel saw with abrasive dust. I did mine inside my garage and I am still finding fine black dust on some shelves and hardware boxes, if it gets damp, it turns to rust. You may also experience difficulty in applying the correct amount of side pressure on the disk, its not like a sawing action where the blade sticks through the steel, more like a slow groove thats gets progressivly deeper as you slide the steel/grinder backwards and forwards past each other.

[Alan_c]

I don't mean upside-down, I mean with the long leg pointing towards the grinder instead of away.

Oh! :o That might be tricky as the surface is not very wide, it will be fine for the front end of the grinder support, but the back end will still need some other means of support independant of the angle. If these two surfaces are not 100% in plane the reslutant cut will have slight changes in the angle of the top surface, although that might not make a difference to the final product.

[hennie]

Hi Alan

Did look into the dust side of things also (would pay Jack overtime to help me ), on every second pass he can clean the table with the extractor.I will also use tape to cover the opening where the blade of the saw is 50 mm wide sellotape (did stick it to the saw but pic doesn`t show).

I should have the balance of the lapp cable by end of this week then I can confirm total cost for them.

[Gerald D]

Hennie, I am nervous about your method. The dust is one issue (grind dust is highly abrasive by definition, and it gets in everywhere - 3+ meter radius). But the other issue is the fact that the rail curves as you split it. How will you make sure that the curved rail is lying flat to your slider?

[hennie]

Option 2 for me.

I have a offcut length of formica top 32 mm thick 3550 mm long.
I would make a support table for this which have to be level (straight over the full length).In the centre I would have my bench drill to drill the holes for the rails and a guide at the back.( will make it during the week )
Question
Gerald if one drill 3,5 mm holes into the rail where the fixing holes would be and use chipboard screw to attach the rail to the formica would it help in some way with the bowing of the steel as one cut the rials down?
(once completed with cutting & grinding one can drill the holes to 12 MM)
32 mm formica top attached to a support table should be stable enough to give nice hight and straight rails and steel are attached over the full length.

[Gerald D]

Hennie, that sounds a lot better. (A chip screw happily grips in a 6mm hole). You are heading for the method used by Alan - he also screwed the rail to "wood" before cutting it down with his karretjie.

[Gerald D]

A video from Brazil:
http://www.kapbrasil.com/trilho.wmv

[orotemo]

Just watched the Brazil video,
This is one sound technique to grind rails. We need some impressions from the cutter, if he could make the measurements in several places along the rail and post it, I'll bet he got the best results yet.

[Valdir Fernandes da Cruz]

Hi all, we improve this method, my brother Wladimir will put a second video for information.

[Gerald D]

Thanks Valdir, we are looking forward to it!

[William McGuire]

Does anyone know if channel iron comes with 1 inch legs? You could then possibly just cut off the spare leg and grind the 45s. It seems as though it would be sturdier than the angle iron and not have any give...

I almost thought of doing it with mine, but the channel legs are 1 3/8 inch

[Gerald D]

You might find a 1" leg channel in your part of the world, but remember that you are looking for a parallel leg if you want the skate to work.

[liaoh75]

I watched the video several times from post #30 but still don't fully understand what I'm looking at. Is the cut being made all way through on a single pass? Is a standard cutting disk being used? Here in Taiwan, there are cutting disks that are made specifically for cutting metal that are just like the saw blades that are used in the "Steel Max" style of saw but made just for an angle grinder. It looks kind of funny and I don't know about the safety factor.

I cut my rails using a home-brew style of contraption similar to several I saw posted by other builders; nothing fancy but I did get some strange measurements after the cutting. One end was almost an entire millimeter taller than the other. I used a 4 meter piece of 7" Channel as my working surface. My Angle iron was well clamped to one edge. I moved the angle grinder and the angle stayed stationary. Another thing I noticed was that there is about a 0.75mm play on the head of the angle grinder I was using which leads me to believe that between the flex in the cutting disk along with the play on the angle grinder head attributed to the variations. The strange thing is the differences were very consistant from one piece of angle I was cutting to another (4 in all). If I were to re-cut I would lean toward moving the angle iron to get a more even cut along the length of the entire angle. Is there anybody that had the same results?

[KenC]

Hi,
Just a idea flashed, What if we bolt + glue a 25 x 25 x 6mm angle on a 60~65 x 6mm flat bar? We'll have 31mm raw height, use the V skate to bring it down to final height of 28mm? (Or other more convenient angle and flat bar sizes would do)

Drilling CSK holes on the angle and tap to get it done correctly.

Edit, Maybe this had been discuseed, please forgive me.

[lumberjack_jeff]

One challenge is that the inside of the 25 x 25 x 6 angle is only 19mm tall (3/4")

Based on my recent use of the skate, I'm not sure I could make the eccentric bushing/bearings/bolt head fit in that space and still have adequate contact between the inside surface of the angle and the bearings.

...Particularly when you consider the boltheads holding the angle to the bar. You could grind the angle without the bar attached, but then there's no guarantee that the assembled pieces will actually be 28mm.

Also, the rail will still need to be surfaced flat before using the skate to grind the bevel.

Otherwise, IMHO, the idea has merit.

FWIW, because I couldn't get my cutting disks to run true on my hand-me-down grinder, I used a harbor freight metalcutting saw, then surfaced the cut angle to finished height with the angle grinder using a grinding disk.

If I build another, I'm sure I could do better. Adjusting the fence to allow the saw to cut true was a fiddly process with much trial and error. The fourth rail looks great.

The first three? Less so, but I think they're serviceable, they'll simply require shimming.

Once this one is done, I NEED to build another. This education should not go to waste. :)

[KenC]

Jeff,
Thank for sharing your experience. Wasn't aware of the clearance as I'd yet to start construction for practical reasons.......

Its true all stock M.S. Angle & Flat bar does have their fair share of tolerance. I'll ditch this idea and concentrate on the MechMate Rail Cutting & Grinding Methode exclusively developed here.

I was impressed by the advance in metal cutting circular saw. Yet to find one off the shelf here... Fortunate for me... or else I would have already dug deep into my retirement fund...

I doubt the circular saw will ever replace the MechMach Rail Cutting proceedure with just one pass. Being more at home with metalworks, I am obsess with a god sturdy datumn, which is difficult with the circular saw... A finishing grind is mandatory is one wish to see accurate and flat finishing.

As such, I'll just have to look away from tha sexy SteelMax circular saw and live with my Bosh grinder...

Damn... Really WANT that toy...

OT, is there anyway I can transform my SkillSaw into a flaming metal chewing mean machine?

[lumberjack_jeff]

Here in the US, the Chinese metalcutting saw is about $90. They also sell replacement blades for $18.

The arbor size is the same as my circular saw and the blade is rated for a max speed which would make it compatible with my circular saw. The only reasons I didn't give it a try;
a) my local Harbor Freight store didn't have any of the replacement blades in stock
b) my circular saw has only the most rudimentary fence. The metalcutting saw has a much better one, which runs the full length of the saw's base. A good fence is not something you can do without when cutting angle.
c) the metalcutting saw has a pretty sophisticated set of shrouds/shields. I think an unguarded circular saw would throw chips (often hot chips) everywhere.

Although others have reported limited success with this, if they had any metalcutting blades in stock, I would have tried using it on my tablesaw.

With good technique, the surface finish was almost, but not quite adequate to use as a skate datum. By the time I cut the fourth rail, I found that if I ripped the rail about 29-30mm, the rail cleaned up very close to 28mm.

A true-running grinder and Pferd disks is probably the best, but having neither, this worked okay.