RE: [SherlineCNC] G-Wizard and Sherline
- Speaking generally the problem with any calculator is that the output is only as good as the input. You have to know enough about the process your using the calculator for to know if the results make sense or not. A calculator is a great time savings device but it is not a knowledge/experience savings device.
Speaking specifically about a feed/speed calculator you have to know enough about the machining process, your machine, the bits your using and the material to know if the numbers you get out of it make sense. There is such a huge rang of bits, materials, machines that it is an impossible task for a calculator to be able to incorporate all of the possible variables. A good example is ‘wood’. Let’s say you tell a machining calculator your routing wood, well what type of wood? Pine will machine differently than MDF or IPE or Cherry, etc. Your bit choice will also play a huge factor. A given bit/feed/speed in pine will react much differently than cherry.
Using the example of a router table with wood from above, take a look at router bits from places like Onsrud and Freud. They will have tables that describe the machining properties of the bit which give you a good starting point (and some of the specifications that you will need for a feed/speed calculator). Similar bits from different manufacturers may have vastly different properties.
Machining metals has similar challenges. Different alloys of aluminum will have different machining properties, different bits and bit coatings can also change things. The type of machine you are using will also make a big difference in what you can do; A Sherline will be better at light/fast cuts while a larger machine might be better using deeper slower cuts.
Even with experience and knowing the parameters of a bit a good machining calculator will only get you in the ballpark; i.e. a safe feed/speed to run at. For optimum results you would still need to do some testing to find out what feed/speed combinations produce the fasted cycle times or greatest bit life or best surface finish. In other words there is no single ‘best’ setting for all cases. For most hobbyist the concern over optimization is not paramount, rather just getting into the ballpark to get a part machined is more important.
I know Sherline has some recommendations for feeds/speeds in some of their documentation. That would be a good place to start. Once you get some experience as to what works better for what you’re doing a machining calculator will be more valuable to you as it will get you into the ballpark faster.
I’m not meaning any of this to sound negative towards G-Whiz or any other machining calculator. It is more of a caution that a novice or less experienced machinist should not expect to trust what numbers such a calculator spits out without first knowing enough to ensure that they are inputting equally good numbers.
From: SherlineCNC@yahoogroups.com [mailto:SherlineCNC@yahoogroups.com] On Behalf Of Martin Dobbins
Sent: Thursday, February 07, 2013 9:30 PM
Subject: Re: [SherlineCNC] G-Wizard and Sherline
I tried it way back in the early days (so it may have improved since then). I found that you have to downrate the power rating so much and then use a great deal of common sense in dropping the numbers that came out that an educated conservative guess was faster and often better! It is not as simple as just horsepower, it is also rigidity, mass, work holding, tool "stick out" and a bunch of other factors that I don't think the software can take account of for Sherline sized machines.
As I said, the software may have improved, and Bob's a good guy- if he still does free trials it might be just the thing for an experiment. Just don't make the same mistake I did and hit a piece of aluminum at even half the speeds and feeds that might pop out with any decent depth of cut if the only thing holding the workpiece is a Sherline vise (!)
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