Machining Hot Rolled VS Cold Rolled Steel

[@mvpmachine]

Watch my next video where I show the effects of machining CRS on a larger scale: kzbin.info/www/bejne/envbY2VultKimaMsi=k1omAeG6FGjDIypk

[@marcellemay7721]

I was taught very early on in my engineering classes that cold rolled steel has a lot of internal stresses because of the cold rolling process. The material is mechanically formed with no heat, hence the name. The hot rolling process relieves the internal stress as the material is formed. The internal stresses in cold rolled are throughout the material and it's pretty unpredictable and shape dependent. And can even be different at one end of the bar compared to the middle of the bar.

[@mvpmachine]

Thanks for watching and commenting!. That is a very accurate assessment of CRS. Unpredictable!

[@preacherpdx5519]

As a newbie working a mill that is probably older than you, THANK YOU. I am having so much fun making things and so much more fun watching all of the grey hairs teach me tricks on KZbin. Again, Thank You

[@mvpmachine]

Thank you for watching and commenting!

[@normtheteacher5485]

You will probably someday need perfect holes in steel to fit bearing races into or a shaft or whatever. I'm kind of new myself. I did a one minute short video on this you may want to watch. You will need what is called a notary table for cutting perfect holes. Got mine at Penn Tool. You are right...milling is a lot of fun and useful.

[@thatsthewayitgoes9]

As 30+ year professional gunsmith, making parts about 10% of time, tool making about 20%. So, definitely not production work; job work. This was SO informative! Usually just keep cutting & file work til have what’s needed ; definitely not running production. But have seen this when making > 3 or 5 parts. Never knew this! How do you machine HRS surface? Fly cutter? Thanks

[@mvpmachine]

Hi thank you for watching and commenting! This is a surprisingly not a well known phenomenon. We use an inserted fly cutter to remove the mill scale on HRS usually .012-.015 depth of cut does the trick and leaves a nice flat finish, better than the CRS finish you get from the mill so its a win win.

[@christopherleubner6633]

Cold rolled has a polarized grain to it, sorta like wood. Hot rolled can have internal inconsistancies. Hot rolled also needs to be descaled, cold rolled may not.

[@RoyLightle-y5p]

Cold rolled has a compressed layer from the rolling process. This gives the cold rolled a higher tensil strength but it looses the extra tensil strength when the compressed layer is machined off. This surface tension is what makes the material unstable for machining

[@mvpmachine]

Roy my personal opinion is that it is more than just a layer that is affected by the rolling process. I have made parts that required heavy material removal on all sides prior to machining and still have had the same effect. Due to the fact that cryogenic treatment solves the problem, I believe the rolling process creates molecular inconsistencies throughout the part and thats what causes the movement. Thank you for watching and commenting!

[@RoyLightle-y5p]

@@mvpmachine I said surface but it probable deeper than that. I was a machinist and I quickly learned the problems with cold rolled.

[@RoyLightle-y5p]

I later earned a mechanical engineering degree and the discussion or the tension in the material was from what I was taught in materials classes.

[@mvpmachine]

@@RoyLightle-y5p I have had a few expensive CRS lessons 😄 myself. Surprisingly a lot of the companies I deal with don't know about this and send almost impossible prints with cold rolled specified.

[@RoyLightle-y5p]

@@mvpmachine They need educating

[@ganjiblobflankis6581]

One component I make comes in 20X6mm CRS bars. Cut to about 3' and clamped to the miller bed then a 4X2.5mm cut taken out of one corner. Finally you weld the ends of these shorter bars and saw them 25mm. After milling, the short bars are going on banana shaped with even a perceptible bend the thick way. On the scale the final component is, the bend is tiny and acceptable and the overall shape and finish is important so it is cheaper to use CRS than dress HRS. It always feels shoddy, but expediency is so often king.

[@mvpmachine]

I feel your pain! We also make a product out of CRS bar stock and have to radius the sharp corners. We made it for years with a lot of scrap pieces then started cryogenically treating the bars after saw cutting and before machining. It fixes the problem but another process to pay for and wait for. Thank you for watching and commenting!

[@MrHanky_YT]

Similar issues are present when bending tight a radius. Hot roll is more forgiving. While cold roll is susceptible to cracking.

[@mvpmachine]

I did not know that, but it makes sense due to the lack of uniformity in the material. Thank you for watching and commenting!

[@jbrownson]

excellent video, I love seeing a guideline like this actually demonstrated to make it concrete

[@mvpmachine]

Thank you Jake!

[@normtheteacher5485]

Good information to know. I have learned to always start a project with stock that is oversized. Lately I've been milling holes in Plate steel on a rotary table for bearing races to fit snug in. Gave up scribing the circle on the stock and then trying to perfectly align the center axis of the table with the center axis of the end mill. Don't have a $100,000 milling machine to do that with. Instead I get the two center axis close and then use the end mill to scribe a circle on the stock that is about 50 thousands smaller than what I need. I plunge cut that out and then lock my Y axis and side mill on the X axis 2 or 3 thousands per 360° rotation. After every rotation I try inserting the bearing race until it fits snug. Then I remove the stock and mill or cut or grind the stocks outer dimensions as needed. I get perfect holes and outer stock dimensions with this method. The hole is positioned perfectly in relation to the outer dimensions as need for the part. Have to start with oversized stock to do this unless one has a $100,000 milling machine. Thanks for your video!

[@mvpmachine]

Hi Norm, thanks for watching and commenting! That is an intresting way to do the bearing holes. The right way to do it is the way that works for the equipment you have available. I started out doing similar things on a manual mill for a product I wanted to make having no knowledge of machining and learned by doing. You get a feel for what works and what does not work. You are essentially doing what a cnc mill does when circle interpolating a hole.

[@patrickbeaumier8616]

Very interesting. Never thought there was that much of a difference. 👍👍👍

[@mvpmachine]

Patrick it is suprising how many times we get prints and material from customers for jobs that can almost not be made from CRS without a ton of extra cuts. This is not a well known phenomenon. Thank you for watching and commenting!

[@donmclean1220]

😊😊😊 😊

[@thehobbymachinistnz]

This is very interesting. Thanks for testing this and sharing the results.

[@mvpmachine]

Thanks for watching!

[@joell439]

Thanks for making this so clear. 👍😎👍

[@mvpmachine]

Thanks for watching!

[@piclife1178]

Great video. I have had problems using scrap bits of hot rolled that have been used as prybars and bent before machining. The locked in stress keeps coming out even when you turn most of the diameter away, very hard to get a straight bar.

[@mvpmachine]

Hi,thank you for watching and commenting! Good point I have observed that as well, but it makes sense that you have stressed molecules along with the un stressed ones. Sometimes bouncing a part off of the ground a bunch of times is enough to " normalize ' it try it next time you encounter that prior to machining. That is an old general motors trick, that is used as a cheap way to normalize welded construction

[@Zircon10]

A leaded steel like 12L14 is free machining and has a higher yield strength than common hot-rolled 1014 carbon steel. StressProof® by Niagra Lasalle is also an option with 100 ksi yield strengths and stress relieve after cold rolling to provide good machinability without warping.

[@mvpmachine]

That is good stuff costs a little more but machines easier. Does not take to welding though. Unfortunately when customers spec a specific material they rarely consider better options, my customers usually say that's what they want deal with it. Thanks for watching and commenting!

[@mackellyman5642]

I wonder if Rifle barrels suffer the same when drilling? Excellent content.

[@mvpmachine]

Mac, I kind of doubt it, drilled holes don't seem to cause this distortion, just open ended milled cuts. Thank you for watching and commenting!

[@1pcfred]

Some rifle barrels are forged. I watched a video of a manufacturer doing it here once. Was pretty nuts.

[@user-hk9ny7qk9u]

Hammer forged

[@1pcfred]

@@user-hk9ny7qk9u can't touch this.

[@frenchcreekvalley]

I wonder what would happen to the cold rolled if you normalized it first. Or--- do they sell normalized cold rolled that might be P&O afterwards? I know that would add to the cost, even more than P&O hot rolled, but It might save overall cost of the project.

[@mvpmachine]

Hi, Thanks for watching and commenting! The problem with normalizing aside from the expense is it will wreck the outside finish and flatness requiring a skim cut and negating the benefits of buying it in the first place. The only process I know of that works and will not change the surface is cryogenic treatment, which I show at the end of this video: kzbin.info/www/bejne/envbY2VultKimaM Another option is using 12L14 steel which is a leaded alloy that costs more than CRS but no headaches when cutting and similar in properties to CRS.

[@frenchcreekvalley]

@@mvpmachine Good points. I had totally forgotten to mention hydrogen atmosphere or vacuum furnace normalizing (to preserve the outer finish. Not cheap, of course, unless--- Back in the 1960's I worked for a commercial heat treating company in a city with lots of small tool and die shops. At the end of their workday, we'd have a constant string of deliveries from them. Enough that we could often consolidate loads so the cost for one individual piece wasn't too bad.

[@mvpmachine]

@@frenchcreekvalley Yes those are good options to preserve the surface too. Not very commonly used for CRS due to the cost and the fact that better material options are available.

[@russellstanley563]

That's what they make coolint for.and grab more of the block with the vice

[@mvpmachine]

Hi thanks for watching and commenting, it would do the same thing with coolant and down lower in the vise. Check out my newest video :m.kzbin.info/www/bejne/envbY2VultKimaM Shows the phenomenon on a larger scale. It has nothing to do with heat.

[@melgross]

I’m not fond of machining CRS either, but sometimes I have to. If you machine to a dimension, you can’t just take down one side, you have to split the amount of cut in half and take half off either side or the piece can bend to one side. Not so much of a problem in really think pieces, but on thin ones it’s a problem. But CRS is somewhat stronger because of the cold roll which compresses the metal somewhat like forging.

[@mvpmachine]

Mel, it is a slightly stronger material but it does not compress evenly throughout the part in my opinion. It sure can be a pain! Thanks for watching and for commenting!

[@37yearsofanythingisenough39]

My experience has been that if you are machining crs and do much more than drill holes in it you better check your dimensions the NEXT DAY, because yes, I have had dimensions change over night on a number of occasions.

[@mvpmachine]

@@37yearsofanythingisenough39 You got that right!

[@timmontano8792]

Generally, when I work with steel it's 1018 cold rolled. My projects don't have to be dimensionally critical. If they were I think I would have used a 3/8" end mill and just taken the extra time and just gone back and forth a few more times till I got the inside dimensions where I needed them. Also, having checked the outside dimensions beforehand and, as high up as you had your metal stock in the vice, even if I got a widening effect at the top of my stock, I could then run my end mill as close to touching the vice as possible and just skimmed the outsides of my stock while it was still in the vice to bring it to the correct width that corresponded with the correct outside-bottom dimension of my stock. Hope that makes sense. Good information. I did not know that there was that much of a difference.

[@mvpmachine]

Thank you for watching and commenting! It did make sense and may be a good solution for this small part, but for larger parts the end mill on the outside would deflect and not be possible. I intentionally did not try to make the slot nice just to focus on the outside changes, but there is a new video I just made that shows the effect on a larger plate part.

[@twm4259]

I know it takes time and time is money but for a small part what about an hour at 400F? Would that be enoigh to relieve internal stresses?

[@mvpmachine]

@@twm4259 no a much higher temp to anneal it but then surface scale would be like the hot rolled steel. So no adding more cost to already expensive CRS. Thank you for watching and commenting!

[@cyber2526]

doing large long parts in cold rolled and you need to hold any flatness you bet you need to do roughing from both sides then finish both sides again seperately, cuz doing both sides once you know its gonna be bent like a banana

[@mvpmachine]

Thank you for watching and commenting! You got that right, all over the map.

[@mikecoppola2123]

At 4:34, On your first test that had the 3 thou vertical runout, do you think running some coolant would help prevent the now thinner material from heating and warping? 3 thou variance with what appears to be about .150 thick walls left behind dont seem too bad at all when she was running dry. Would love to see 2 pieces of CRS machined in the same vise with the same end mill, 1 with coolant, 1 without.

[@mvpmachine]

Thanks for watching and commenting! There really is not much in the way of meaningful heat transferred to the part dry milling as the majority of the heat comes off in the chips. Most machinists over use coolant with carbide toolong. Those parts may have been 90 to 130f at most after cutting, no where near what it would take to move anything. I have a newer video that shows the CRS movement on a larger scale shown here: m.kzbin.info/www/bejne/envbY2VultKimaM

[@JustaCommonJoe]

I'm a basic home project tinker machining hobbyist (By no means an engineer or machinist!) and noticed the discoloration of the shavings in the video. In your expert opinion do you think that running coolant or adjusting feed speeds and depth increments would change your end results at all? I appreciate your expertise in the machining/milling process and the most valuable information that you provide. I thank you, and I was wondering if my inquiry carries any pertinent merit. Please continue your beneficial tutorials, and I will be sure to continue to watch and learn from them. 👍👌

[@mvpmachine]

Hi, that is a good question! The idea is to have the heat come off in the chip and not be transferred into the workpiece and that is what you see. If a chip is solid blue or black then it likely is a worn out end mill or a poor feed and speed selection or too light of a cut. If the chip has some yellow left in it it means the end mill is good and sharp and the chip has more heat it can take with it if needed. Coolant is terrible for most modern coated carbide end mills and will cause premature wear. The coatings are designed to perform best in high heat conditions and will experience thermal shock when coolant is used. The parts in this video did not get hot enough to cause any distortion, and would be the same dimensionally if coolant was used but end mill life would suffer. I have a video coming out about this topic very soon. Thank you for watching and commenting!

[@normtheteacher5485]

Sometimes when milling I will get different colors of chips depending on where the cutter is cutting. Sometimes blue, sometimes brown, sometimes just the color of the steel. I'm not sure, but my theory is that the stock is not a consistent alloy all through out the stock. Some areas machine better and easier than other areas in the same piece of stock. Could also be inconsistent heat treating throughout the stock. Case hardening is a good example of where this is done on purpose. The outer layer of metal is harder than the core.

[@JustaCommonJoe]

Thanks for the update. I had noticed those chips and wondered because I've seen alot of machining vids that use coolant and don't. I myself never do for what I do. I've always taken light cuts at a slower feed speed and moderate bit speed. It takes more time, and in my book extends the life of bits. But all said and done, if it requires more time it's worth the positive outcome. Thanks again!!@@mvpmachine

[@JustaCommonJoe]

That all makes sense. I always assumed that colored chips meant dull bits or too deep of cut, or too fast of bit speed. I guess that the end if the bit shows no color change, the operator settings are within parameters. Thanks for the input!!@@normtheteacher5485

[@normtheteacher5485]

You could be right. Dull bits, too aggressive cuts produce extra heat. Extra heat discolors metal.

[@ironcladranchandforge7292]

Internal stress on the cold rolled, which is being relieved as you machine it. It's basically springing on you.

[@mvpmachine]

I agree as simple as that. Thank you for watching and commenting!

[@heregulmithal7063]

Excellent informative video

[@mvpmachine]

Thank you!

[@sillytoy1]

Try putting the piece deeper in the vise. You could use cold rolled 1018 that is ground has no scale and much more stable. Costs a bit more but if the jo calls for it do it. Used all of the above when I had my shop, retired now.

[@mvpmachine]

Deeper in the vise would make it worse. Then when it springs the inside and outside would both be wrong. Ground CRS may help a little but if you check out our latest video I kind of did the same thing and no benefit. Thank you for watching and commenting!

[@edwardbelfiglio7299]

The term "Cold Rolled Steel" is completely misused! Cold Rolled Steel only applies to plate, sheet and strip!! Bar stock in rounds, squares, flats, octagons , hexagons and other bar shapes is COLD DRAWN, not sold rolled!

[@mvpmachine]

Edward you are correct, except rectangular bars are also rolled, other 1018 shapes round hex etc. are drawn and incorrectly referred to as CRS.

[@smnkm4ehfer]

"Cold worked" is usually the catch all

[@andrewmicas4327]

UK we called it BDMS bright drawn Mild Steel, all good fun as an apprentice, skim one face of a thin flat and take out of vice , it went like a banana .

[@jorickferies2299]

Thank you for those explanations and sharing that long video. I've just heard about that phenomena in a machinist company i was working with recently. I was wondering, does pro machinist includ that phenomena since the beginning of their cutting organisation to correct the best they can, also is annealing a common process to avoid this for expensive parts sometime ? Just curiousity of how you guy's work. Big thanks from France. Have a good day sir.

[@mvpmachine]

Hi, thanks for watching and commenting! Unfortunately it is not a well known phenomenon. I have been doing this for over 25 years and we are routinely supplied with 1018 material from customers for jobs that it is not appropriate for. Annealing will not work as it changes the surface of the material and also the strength of the material. Cryogenic treatment is the only solution for pre treating that will not alter the material strength. Many times when we quote work we make sure we specify 1020 if possible to make sure we do not wind up with the extra expense and time.

[@patrickday4206]

Difference between cold rolled and cold forged ???

[@mvpmachine]

Cold rolling is exactly as it sounds the cold newly made material is rolled and compressed between rollers to get it to its finished size. Cold forging is a process of making parts using dies, the part is pounded between dies until the desired shape is achieved no heat is used. Thanks for watching and commenting!

[@simpleman283]

I see you let Joe Pie hang out in the shop.

[@mvpmachine]

I wasn't sure who that was then I searched and saw his channel then subscribed. Thanks!

[@jimsvideos7201]

Good show, thank you.

[@mvpmachine]

Thank you sir!

[@Iowa599]

It seems like it must have internal stress that are released upon machining. What if you heat temper it prior to machining it?

[@mvpmachine]

It would work but cause surface scale that negates the benifits of using the cold rolled steel. Thank you for watching and commenting!

[@1pcfred]

All bets are off when you heat treat. You can pretty much guarantee dimensional changes then.

[@Iowa599]

But after (de)treatment the dimensions will be stable.

[@1pcfred]

@@Iowa599 it'll be what it'll be. Which won't be what it was. When you heat steel up it's like you hit the randomizer button on it. It never cools back down to the original dimensions. Now there's people that can play the warp and figure where things are going to end up. But that ain't me. I can only tell you it will distort.

[@Iowa599]

@@1pcfred ie: overheat an engine, head gasket surface.

[@x1xBryanx1x]

Good info. Makes sense.

[@mvpmachine]

Thanks for watching!

[@lumpygasinavacuum8449]

Thanks I learned something

[@mvpmachine]

Thank you for watching and commenting!

[@Tome4kkkk]

It's not a layer. Especially not in thin walled geometries. There are rolling and forging visualisations on KZbin. Take a look.

[@mvpmachine]

I agree it is through the whole part! Thanks for watching and commenting!

[@ahbushnell1]

Can you heat treat cold rolled before to reduce stress?

[@besssam]

In theory yes, you can spend more to stress relief it at 600C, but as it heats and softens the residual stress will likely warp it, so might as well use hot rolled in that case.

[@mvpmachine]

Cryogenic treatment solves the problem, I show in my newest video but can be pricey if you don't have some quantities. Thanks for watching and commenting!

[@1pcfred]

Yeah screw the material up ahead of time. Better living through lowered expectations. Stress is the big killer.

[@christopherleubner6633]

Yes you can do this, but you may as well use hot rolled as it will have surface scale.

[@ahbushnell1]

@@christopherleubner6633 I didn't know that. Thanks

[@richb419]

hi good video, if you normalize the cold roll will it stay on dimension?

[@mvpmachine]

Hi Rich, I suspect it would help but it is not a common practice likely due to surface considerations. I know Cryogenic treatment for 2 days (nitrogen bath) works well but a little pricey especially with small quantities. Thanks for watching and commenting! Tim

[@richb419]

thank you for getting back!@@mvpmachine

[@AnthonyTobyEllenor-pi4jq]

@@mvpmachine "" I know Cryogenic treatment for 2 days (liquid nitrogen bath) ""

[@ColKorn1965]

Cold rolled warps and twists in unbelievable ways when it's machined.😢

[@mvpmachine]

Easy to cut hard to make right dimensionally! Thank you for watching and commenting!

[@larryscott3982]

What about the width of the slot?

[@mvpmachine]

The slot opened up at the top by .014" or so as the material sprung the slot got wider on the CRS but not the HRS. I was trying to focus on the outside because it is possible to leave enough stock and rough and finish the slot and have it come out fine as long as it is not trapped in the vise where you are cutting. If held deeper in the vise both inside and outside dimensions would be sprung and change as soon as the vise is released. Thanks for watching and commenting!

[@QwertyCanada]

Very informative; too much background noise though. Thank you

[@mvpmachine]

Thanks for watching! I am working on a solution for the noise, its tricky in a shop though.

[@chrimony]

@@mvpmachine It takes extra work, but audio processing is a thing. There are noise filters to remove the background hum of machines, and you can lower the audio of parts where the machine is going full bore.

[@phiksit]

Put the first part in the vise and squish it true 😁

[@mvpmachine]

😆

[@simpleman283]

👍good information.

[@mvpmachine]

Thank you for watching!

[@arrealhandymanservice4459]

Man I thought all metal had scale on it I’ve had some tubing soaking in acid and I been grinding thinking it was scale and it wasn’t lmao I should have known because the metal did not have the dull gray look to it I just assumed

[@mvpmachine]

Some steels are pretty clean but can get a little crusty from hunidity causing a little surface rust. Thanks for watching and commenting!

[@HFG]

👍🏼👍🏼

[@meanman6992]

Good grief you could have just said from the get go cold rollled has more internal stress’s than hot rolled which can cause it to warp when you cut a lot from cold rolled.

[@mvpmachine]

You are right I could have but that would have been a 10 second video. Thanks for watching!

[@bob_mosavo]

Thanks 👍

[@mvpmachine]

Thanks for watching!

[@BruceBoschek]

Sweet dog. 🙂

[@mvpmachine]

Thanks Bruce! That's my pal Butters he is an Olde English Bulldogge, he comes to work with me every day.

[@BruceBoschek]

Super! ❤

[@TB-zw7dt]

Temper, temper. Controlling your temper is always a good idea.

[@mvpmachine]

If you are refering to heating the part by dry milling you are incorrect these parts did not get hot, the heat comes off in the chip. Collant kills carbide endmill life and is unnecessary when milling most steels. I use air blow to evacuate chips to prevent re cutting. I will have an upcoming video on this topic very soon. Thanks for watching!

[@1pcfred]

Slots O luck.

[@cheekkeith74]

When your efi software goes obsolete... then what?

[@mvpmachine]

What is EFI software?

[@cheekkeith74]

​@mvpmachine Sorry. This was supposed to go to a different video. Don't know how it ended up here.... Please disregard.

[@DigitalVideoFromOz]

Info was very good, but you would do everyone -- including yourself -- a favor if you got yourself "Miked-up" better. Microphone, not micrometer.

[@mvpmachine]

Hi Thank you for watching! I did somewhat fix my audio in my latest video, I have a new noise cancelling mic. It sounds a little tinny when the machine is running but better.

[@DigitalVideoFromOz]

@mvpmachine Well that's great. Good job, you are are too good to have a poor mic getting in the way. My career is in television news so I notice mic's. I will watch more of your stuff.

[@mvpmachine]

@@DigitalVideoFromOz Thank you!!!

[@whydotheyneedtoknow718]

Please speak clearly and show the micrometer views side way on.

[@mvpmachine]

Thanks I'm working on the audio issue. KZbin keeps "fixing" my audio when I upload and it quiets it down likely to equalize it to the machine sounds.

[@Je.Suis.Flaneur]

Please learn how to record audio. Your voice is almost unhearable. I've got my volume at 100% and you are not easily audible. Thanks for your video.

[@mvpmachine]

Sorry Mark I'm working on it I turn it up full tilt on editing and KZbin turns it down when processing the uploaded videos I think trying to equalize the machine noises with the rest of the video? Thank you for watching and commenting!

[@clockworkvanhellsing372]

​@@mvpmachine Audacity is a free audio edeting software. It has a feature that detects noise pattern and removes that noise from the audio track. The usage can be leaned in 5 minites and you only need to record a bit of background noise (a few seconds, longer is better) before you start speaking to use that feature. It would significantly improve the audio quality for future videos.

[@mvpmachine]

@@clockworkvanhellsing372 Thank you for that!! I will try it tomorrow on my next video.

[@toddholldorf9494]

My hearing isnt the greatest, but I heard him loud and clear on 7/8 volume. There is a slight background noise but not bad. May be your speaker set up.