Cold rolled steel?

[P. Waller]

Bloody hell
An expensive online source such as Speedy Metals will sell you 1 foot of 1" diameter 1117 CF for $9.51 and this is a cut length price, it is likely that a metal supplier will sell you 12 foot uncut bar feeder lengths for the same amount or less.

Does not your decorative home project deserve $25.00 worth of material?
https://www.speedymetals.com/pc-329-8233-1-rd-cold-finished-1117.aspx

 

[jdedmon91]

On the face of it, it does make sense, but availability is a big issue with most folks, it seems; surely we could all order from a convenient online source, such as Mc Master Carr, but it gets pretty expensive. I am personally fortunate to have cleaned out all the remnants of stock when I sold my business and taken them home, my very own little scrap yard, and can still go back to my old shop and beg material when needed, in exchange for such as cutter sharpening, etc.
Most hobbyists are not so fortunate, and must, by necessity use what comes to hand; by experience, they will learn to deal with less than ideal materials, and learn which cutting tools and lubricants lead to an acceptable finish, and also, they need to learn the use of files and abrasive cloth; cutting tools are not the panacea when it comes to finish.
Another thing that I have harped on several times previously is the choice of carbide inserts that hobbyists seem to gravitate to for reasons of economy, handiness, and utility; I am speaking of the parallelogram shaped (negative rake) inserts, they do not lend themselves to nice finishes to say the least, fine for roughing on a machine with sufficient power to effectively use them, machines, for the most part the hobbyist does not possess. A free cutting (positive rake) insert goes a long way to solving finish quality problems. I use nearly all TPG (positive rake) 300 and 400 series inserts for my lathe work except for work done on my 9" Monarch, where I use all HSS tools.

Well I beg to differ on negative inserts. Your limitation is HP of the machine and the relationship of the material. I regularly machine 8620 because I have some of that material. My tool of choice is a MCLNR 163 tool holder with a dovetail cut in to be direct mount in my QCTP.



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[Pcmaker]

I just carbide to cut grade 5 bolt at around 600 rpm, and the finish is super smooth, almost polished

 

[ddickey]

Because there is some hardness to the bolt more than likely.

 

[P. Waller]

I just carbide to cut grade 5 bolt at around 600 rpm, and the finish is super smooth, almost polished

Do not confuse spindle speed with Cutting Speed
Rpm means virtually nothing without a diameter, this is why tool manufacturers and guide books describe cutting speed in SFM/MPM.
You will be well served if you make all of your decisions on spindle speed related to Cutting Speed.
For some reason many find this difficult, it is the simplest calculation that you will do in the machine shop yet possibly one of the most important parameters.

If MH cut speed tables recommend 100 Feet Per Minute for high speed steel tools when cutting low carbon steel start there.

Desired SFM X 3.83 ÷ by the part or tool diameter = RPM
For instance a 1/4" diameter part turned at 100 SFM would be 382 ÷ .25 = 1528 RPM's
A 1" diameter part at 100 SFM cut speed would, to no ones surprise, have a spindle speed of 383 RPM's
The cutting speed tables assume that the conditions are ideal, rigid work holding, robust machine/tool holding and a coolant/cutting oil flow up to the task.
Machinery's Handbook cutting tables were not written for hobby type machines in hobby settings so start slow and go up from there.

One of the most common discussions on this forum is "poor surface finish using carbide tooling".
With carbide tooling this is mostly do to a lack of cutting speed, a common coated insert for mild steel would be used at 300+ SFM cutting speed minimum in order to achieve a nice finish.

6061 aluminum ring turned at 460 SFM, the diameter is 14 1/2"
460 X 3.82 = 1750
1750 ÷ 14.5 diameter = 121 RPM's
I only had a choice of 125

 

[stupoty]

Some of the Hot rolled steel I've had has been slightly less than round

Stu

 

[Tozguy]

We have been referring to a 'good' surface finish without really describing what we mean. I am just a beginner hobbyist compared to most of you but to me it all can have an impact on finish (ie. choice of material, tools, feeds and speeds, d.o.c.)
I envy a professional with adequate equipment who knows how to get to the desired technical finish quickly enough to make money at it. In contrast I will not necessarily start with the best of choices of tools, materials and techniques. The reasons for getting a 'good' finish are sometimes just as mysterious to me as the reasons why the finish is 'bad'. It is a great learning process however and have found that gummy aluminum is worse than any steel I have tried.

 

[BaronJ]

Hi Guys,

As I previously said horses for courses ! I agree that some aluminum is horrible to machine. A good lubricant can make all the difference between stuff that welds itself to your toolbit and getting a clean cut.

I read an article on line a few weeks ago about some trials machining these gummy materials, in particular copper and brasses as well as aluminum.
The trials included coating the surface to be cut with various substances, including permanent markers, Pritt adhesive among others.

Now I've had an opportunity to try this technique out, and whilst not under laboratory conditions, does seem to help. The build up of material on the cutting tool seems to be much less or not at all.

What the researchers said was by coating the surface of the material to be machined, it caused the material to behave as if it was a much harder material. The report does not make any mention of whether lubricants or cutting oils were used, only the application of the items mentioned earlier.

 

[stupoty]

stuff that welds itself to your toolbit

I have issues with parting tool inserts , If i have cut aluminium with them then I find thay are no good for steel any more.

I have also noticed that I have to clean up my HSS turning tools after aluminum or they suffer in a similar way.

the WD 40 aluminium lube does seem to help stop the aly glueing itself to the tools a bit.

Stu

 

[Dan_S]

It is the material that is important not the finishing process as far as machining goes.

I would say the finishing process isn't important, its more like material first then the process/heat treat.