Ground Rectangle Bars?

[Nerdlinger]

Hi Everyone!

Forever we have been buying 12' long cold drawn bars of 4140...about 1"X2". We saw cut the blanks to about 2" long and do some machining to them, send them out to heat treat, hand grind the four outside CD surfaces, tumble, and chrome plate. In an effort to get rid of the hand grinding we started face milling the outside surfaces before HT. It totally works but is nearly as labor-intensive as hand grinding...(load, cycle start, flip, cycle start, flip, cycle start, flip, cycle start.) I've tried standing the parts up in a vice, going around the outside profile with an end mill, flipping over, and trying my best to line up the mismatch lines but to no avail. The tumbling will not really erase any mismatch line more than .0002" or so.

I am starting to look for a grinding service that we could ship the bars to and have them grind all four sides of the bars like one would do on a thickness planer (for wood) but with a grinding belt. Like a Time Saver or something.

Is that the best route to go or is there some other surface finish service I don't know about. The overall dimensional tolerances are not very tight...+/- .005" and the surface finish does not need to be a mirror...just "smooth" so we don't see pits after vibrating and plating.

Thank you!

 

[sfriedberg]

I don't have a specific recommendation, but there are suppliers of pre-cut, pre-ground blanks whose ads claim their prices are pretty close to the raw material cost. Maybe get your blanks that way, instead of sending them out for grinding?

 

[MaxPrairie]

What hardness are you heat treating to? Mcmaster sells 1x2 prehard and ground. They do not have grinders, so they are buying it from someone...otherwise this sounds like a blanchard grind job. Orrr option 3, make yourself a set of cut through soft jaws. Facemill and swipe two edges, flip over and rotate 90 degrees and hit the other 3 sides. I like cut through jaws because you can see how much stock will be removed from each side so no need to set a new offset. Unless you have end holes, this is a 2 op part and out to heat treat.

 

[Nerdlinger]

How many of these blanks do you need a week? It sounds like a long time job, would it be worth the effort to make a machine sort of like a double-disk grinder but with belts for your purposes?

You’re right : it IS a long-running job. I think the Time Saver machines are the closes thing I could think of and that might not be impossible. I’m just hoping there’s someone already better set up than me. Thanks!

 

[Nerdlinger]

I don't have a specific recommendation, but there are suppliers of pre-cut, pre-ground blanks whose ads claim their prices are pretty close to the raw material cost. Maybe get your blanks that way, instead of sending them out for grinding?

I’ll check it out. I would probably have to send them the raw stock because it’s a custom size…7/8” x 1-3/8. Thanks!

 

[Nerdlinger]

What hardness are you heat treating to? Mcmaster sells 1x2 prehard and ground. They do not have grinders, so they are buying it from someone...otherwise this sounds like a blanchard grind job. Orrr option 3, make yourself a set of cut through soft jaws. Facemill and swipe two edges, flip over and rotate 90 degrees and hit the other 3 sides. I like cut through jaws because you can see how much stock will be removed from each side so no need to set a new offset. Unless you have end holes, this is a 2 op part and out to heat treat.

Only about 30HRC, but it’s a custom size…7/8” X 1-3/8” d’oh! Unfortunately there IS work to do on both ends…so all six sides get work. Thanks!

 

[MrWhoopee]

I you're not grinding the ends, send cut stock out for Blanchard grinding. They can load a bunch of them on a 36" or 48" chuck and a Blanchard will make quick work of the stock removal.

 

[Garwood]

Friend of mine does a ton of graining for other shops with his timesaver. IMO it's not really great at knocking down steel parts with mill scale. The edges cut more than the middles, dimensions are hard to hold. The process is great to put a specific finish on material that's already smooth. Stainless and aluminum look amazing, but steel not so much.

I think you want a blanchard or a double disc grinder. Double disc grinders are insanely expensive so that probably leaves you with Blanchard.

 

[eKretz]

Find someone with a surface grinder that has a great big table and have them do a whole batch at once. You can do the ends that way too, since you can put them all on the table at once they will be easy to block in so they can't tilt.

 

[Comatose]

Agreed, a wide belt is tough to use as an abrasive planer for wood even (compared to a planer) unless you're running a steel drum and no platten. I can't imagine trying to do meaningful metal removal with one. Great for knocking off plasma scale and rust. Meaningful steel removal eats through belts.

How many are you talking per day/week/month? There are solutions at 10pc/day and solutions at 10000pc/day, but they're not going to be the same solutions.

When you say you're hand grinding the surfaces now, do you mean "hand load onto an automatic surface grinder in batches" or do you mean "crankity crankity crank"?

We have a produce we make that starts life as a four sides ground blank, more or less the same idea. I gang then up on a medium-big automatic surface grinder (16x32) that fits 60 at a time, and let that nibble away at them while we do other things. It's not too bad for a hundred or two a day.

I've looked casually into the ground blank suppliers, but it's never, ever close to the cost of raw material, unless you get your material at McMaster.

 

[Nerdlinger]

Yeah I’ll have to look into Blanchard…we’re talking 300 parts per day or so. I see what you’re saying about the deflection to be expected from a less-than-infinitely-rigid drum on the Timesaver. I never thought of using a surface grinder as a production machine like that because we really only use them in the tool room but, like you guys have said, we could lay out a whole bunch of parts and come back in 30 min or whatever and flip em over. Hmmmm…

Comatose - I mean 6” wide X 168” long grinding belt machines and literally holding the parts in your hands to grind the outer four sides.

Thanks!

 

[MaxPrairie]

4140 prehard is 28-34 HRc, it can be purchased as plate or flats in DCF. If you start with oversize stock, there are plenty of solutions to hold onto less than 100 thou so you could run around them and face off the backside. If you had a 4th or horizontal you could really be cranking these out and be a lot less labor intensive.

 

[Nerdlinger]

4140 prehard is 28-34 HRc, it can be purchased as plate or flats in DCF. If you start with oversize stock, there are plenty of solutions to hold onto less than 100 thou so you could run around them and face off the backside. If you had a 4th or horizontal you could really be cranking these out and be a lot less labor intensive.

Yeah that’s, true…I could talon grip those suckers. Thanks!

 

[Garwood]

4140 prehard is 28-34 HRc, it can be purchased as plate or flats in DCF. If you start with oversize stock, there are plenty of solutions to hold onto less than 100 thou so you could run around them and face off the backside. If you had a 4th or horizontal you could really be cranking these out and be a lot less labor intensive.

9 out of 10 times material is way cheaper than labor.

 

[Bill in PA]

You might look for a shop with a large knife (industrial knives) grinder. The chuck will be around 8-10" wide and 10-18 FEET long. With a vertical head, it can skim the bars quickly.

Precision Knife Sharpening & Knife Grinding

Bill

 

[MaxPrairie]

Yeah that’s, true…I could talon grip those suckers. Thanks!

Yes you could also throw 20 thou radii on the 4 corners and a 10 thou chamfer on and skip the tumbling step. Every time I get a model file when programming the profile cut I add a radius so the endmill doesn't kick a burr back when turning the corner.

 

[CarbideBob]

How square is the stock and how square does it need to end up?
Flat grind in a Blanchard or SG on a chuck will make opposite sides flat to each other but not square.
We would grind side 1 on the chuck, put in a fixture to grind side 2 square, grind sides 3 and 4 on the chuck.
Bob

 

[eKretz]

How square is the stock and how square does it need to end up?
Flat grind in a Blanchard or SG on a chuck will make opposite sides flat to each other but not square.
We would grind side 1 on the chuck, put in a fixture to grind side 2 square, grind sides 3 and 4 on the chuck.
Bob

Personally if it's a bulk quantity of parts with squareness tolerance that's not crazy tight, (he made mention of the fact that they had previously been hand grinding these surfaces on a belt sander) I might try grinding the first two opposite sides parallel then blocking in tight with good square blocking at the ends and sides and grinding them all in at once. Good square blocking on both ends and at the sides with the blocks lightly tapped to snug after the magnet is on should act pretty much like a grinding vise.

I would do it in similar fashion to you if I needed tight tolerances. I usually grind two sides parallel first, then square up, but either way works. This doesn't sound like that's the case though.

 

[michiganbuck]

Going from 1 x 2" down to 7/8 x 1 3/8" is a mile of stock by any method.
Agree how square, size limits, and finish size of the rectangle would be a great help.

to reduce the needed rough take might be a concern...perhaps addressed with the original stock size selection. Rapid getting down to +.020 or less
, or roughing two sides to square and size?

 

[CatMan]

Can you find 1" x 1 1/2" rectangle stock instead? Does that leave enough to clean up to 7/8" x 1 3/8"?