Feeds and Speeds in Gibbscam

[canyon289]

When using Gibbscam do you use the default feeds and speeds or do you look elsewhere?

I ask because there's a lot of conflicting advice, and products, about what depth of cut, stepover, feeds and speeds to use and it's quite confusing, especially once you throw in different tools and materials into the mix. If I could start with the suggested ones in Gibbscam it would help greatly.

Thanks in advance

[txcncman]

This question comes up in all of machining, not just when using GibbsCAM. This is why a fellow cannot step off the street and with the magic of computers be a machinist in an hour...or a day...or a week...or a month...or really even a year. This is also why, even though much of machining seem scientific, it is still more art than science. There is no computer software yet that can take into account as many variable as the trained and experienced human brain can and make adjustments for those variables. But, "they" are working on it. To answer your question directly, yes, you can start with a default setting. It will either work, or it won't. Either you will break a tool, or scrap a part, or be inefficient. Or, you won't. The smart thing to do is to educate yourself of the recommended speeds, feeds, chip loads, axle depths of cuts, and radial depths of cuts and the formulas associated with these things. The best place to start is actually a machining class. Then there is the Machinery Handbook "Machinist's Bible". Then there are the tool manufacturers specs. Once you put these things together, you will have a reasonable starting point for your machining data. But even this will have to usually be adjusted when placed into application to compensate for chatter, tool deflection, part deflection, secure work holding, and other variables.

[canyon289]

Hey Txcncman, Thanks for the reply!

To let you know where I'm at, I'm a dirt poor mechanical engineering student at a school that just bought two Haas machines. I got tired of learning how to design parts but not actually make them, and decided to just learn on my own since I biffed up my degree. Silly me thinking Mechanical engineers are supposed to get their hands dirty these days.

So I bought the Machinerys handbook a while back, albeit the 18th edition from 1968, and have read up on speeds and feeds. I've also found the formulas online to calculate them manually and when manual machining they work great. With the LeBlond lathe and Bridgeport mills I can get really clean cuts conventional milling. The one thing with manual machining though is I know when they're not working with just feel and smell and I can back off. With a littler over one years experience by no means I'm a pro but I've stopped breaking tools nearly as much as I have when I started.

The trouble I'm having with CNC machines is that once I punch in those settings the machine will plow on, broken tool or not. On the economic side I can't hold a job, get good grades in my classes, and learn how to weld and CNC. Whatever money I can scrape together on the side goes into these tools and I can't afford to buy new ones everyday. Lastly the machines are new and nearly no one knows how to use them at my school. Since my state, California, is basically bankrupt these machines are the nicest ones we've gotten in a while and everyone is eyeing them. I need to establish myself as someone who can competently use the machines and I have to do it fast. If someone sees me breaking tools all the time they're going to kick me off and that's the end of that. I'll be stuck learning useless equations all day instead of learning what I want to, which is how to actually make things.

Sorry for the long winded story. Like you said it takes experience and I want to start asap.

To restate my question, I was planning on taking medium to light depth of cuts to ensure I don't break my tools. I'd mostly be cutting mild steel and aluminum, MAYBE stainless if I can find some stainless scrap in the trash can. I'm not in a production environment so cycle time doesn't really matter and since I'm just starting, and don't have all the proper tools, if I can get within 20 thou I'll be thrilled.

Are the Gibbscam recommended values good conservative starting points in your experience? If you don't know though don't worry. Hopefully I can tell you in the next month whether if they are

[cadman]

Originally Posted by canyon289 Are the Gibbscam recommended values good conservative starting points in your experience? If you don't know though don't worry. Hopefully I can tell you in the next month whether if they are

The feeds & speeds database in GibbsCAM is from the Machining Data Handbook. Yes they are good starting points, but there are a multitude of parameters that will affect feeds & speeds, such as the tool (material, coating, flute form, etc..), work material and condition, tool holder, machine, fixturing, the toolpath itself .......

There really is no shortcut for experience.

[canyon289]

Thank you for the advice,

Don't worry, I know I have to actually start making chips to learn how to do it properly. It's why I'm here in the first place, I got really tired of reading about machining in books and decided to just get dirty and learn it first hand.

I was just looking for a general starting point and it looks like I've found it with Machinery's handbook and Gibbscam. I'll just use that for now and figure it out from there.

Thank you again for the replies

[txcncman]

I appreciate your efforts to learn and your decision to "get dirty". My biggest disagreements in manufacturing have not been with fellow machinists. They have been with engineers that have no reality to base their ideas on, only what they were told in college. I can give dozens of examples.

My advice is that if you cannot build it, don't design it.

[canyon289]

Originally Posted by txcncman I appreciate your efforts to learn and your decision to "get dirty". My biggest disagreements in manufacturing have not been with fellow machinists. They have been with engineers that have no reality to base their ideas on, only what they were told in college. I can give dozens of examples. My advice is that if you cannot build it, don't design it.

Sad thing though is that I could have gotten through my entire degree without getting a drop of grease on my hands. I'm very frustrated right now that I spent tens thousands of dollars and four years on an education that really isn't teaching me how to actually make anything, just run numbers all day. It's a big reason why I appreciate yours and others help on this forum. It's really the only way I'm able to fill this enormous gap in my knowledge.

Also a big reason I'm posting here for feeds is speeds is cause I'm broke for paying for college AND not being able to get a full time job because of classes. The less tools I break while starting out the better. I still have to buy my own holders, calipers, edge finders and whatever other expenses that I don't even know about right now. Thanks for the help

[DALACHEAX1]

In my experience the cad/cam speeds and feeds arent even close, just a very uneducated guess. To figure your speeds and feeds you need the recommended SFM (surface feet per minute) and FPT (feed per tooth) or IPR (inches per revolution) of your selected tooling. Also the length of the tool, the holder and how ridged the setup is all play a factor in machining a part with tight tolerance and with decent tool life in an acceptable amount of time. I myself love it when program managers/mechanical engineers bid a job and recieve it with absolutely no idea of what is required to make it happen!

[canyon289]

Originally Posted by DALACHEAX1 I myself love it when program managers/mechanical engineers bid a job and recieve it with absolutely no idea of what is required to make it happen!

At the risk of being banned from these forums, or even just trolled, I'll be honest and tell you that just a year ago, in my junior year of engineering, I literally thought that machining these days was as easy as hitting print on in Word. This is why I'm here now though. After it dawned on me that the stuff I design in SW doesn't appear before my eyes. I'm trying really hard to get competent in this so when I make bids or ask someone to make a part I KNOW what I'm asking for.

Another HUGE thing I realized is that all engineers are completely useless without fabricators, COMPLETELY USELESS. No one ever drove a Catia model to work, or flew in a Unigraphics plane. I was pushed into a bachelors though (everyone needs a bachelors!!!! sigh) and if I had a time machine I'd go back and get some heavy fabrication experience first before starting out in college. All I can do now is figure this out as fast as I can. Again thanks so much for helping me.

To clarify my question though, right now I don't care about surface quality and my tolerances are as wide open as 1/16th of an in. I would like to start making cuts as cheaply as possible, which means breaking and wearing down tools minimally. High tolerances will come after, right now I just need to start making chips.

[DALACHEAX1]

Originally Posted by canyon289 To clarify my question though, right now I don't care about surface quality and my tolerances are as wide open as 1/16th of an in. I would like to start making cuts as cheaply as possible, which means breaking and wearing down tools minimally. High tolerances will come after, right now I just need to start making chips.

Machine type? Material type? Machine horsepower? Actual tooling selected, including # of flutes, carbide cobalt or HSS? Standard or High performance? Answer these and Ill help as much as I can, Im working on connecting rod for a 315 ton press with these dimentions 9" thick x 37" wrist pin to crank pin center, so Ive got some time! LOL

[DALACHEAX1]

Here is some basic s&f information that I have been using for years.

HSS drills in carbon steel- 70sfm(standard) .0005fpt (1/32th thru 1/8th) step up your fpt .0005 for every 1/8th increase in drill size. Peck drilling works best and a peck value of .010 for 1/32 thru 1/8th, step up .010 peck value for every 1/8th increase in drill size. Example; .250 drill = .020 peck, .500 drill = .040 peck, 1" drill = .080 peck. Be aware you may hit your machine horsepower limits using larger diameter drills.


Solid carbide endmills/roughing,pocket in carbon steel- 250sfm 1/2 the diameter depth and width of cut (axial and radial) fpt varies according to the actual tool geometry but here uis a baseline for you. .500 endmill = .0025 per flute, increasing fpt .001 for every 1/8th increase in diameter. Note; long length of cut endmills require about 30% less sfm and about 50% less fpt to be sucessful and avoid breakage.

I will post more as I can. Bruce

[mcphill]

Have a look at Bob Warfields G-Wizard:

GWizard: A CNC Machinist's Calculator for Feeds and Speeds