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Browsing articles from "February, 2011"

Exploring Ramping and Interpolated Holes with G-Wizard’s New Mini-Calcs

Feb 26, 2011   //   by Bob Warfield   //   Blog, Software, Techniques  //  No Comments

I’ve just finished adding a new feature to the G-Wizard Calculator that I call “Mini-Calcs” for release 1.040. Mini-Calcs are little popup feeds and speeds calculators for special situations. We already had one popup for calculating ballnose cutter stepover to achieve a particular surface finish. I’ve just added two more–one is all about interpolated holes and the other is about ramping. Both are common CNC operations that may be used to get a cutter down into a pocket or in the case of interpolation, this is an effective way to use an endmill to create a hole of a particular size. There are a lot of trade-offs around making holes with interpolation, but more on those in a moment.
The Mini-Calcs are accessed directly under the Tool Definition (where you specify tool diameter, flutes, and so on):

The three Mini-Calc buttons are right under where you specify Tool Diameter and Flutes…
Let’s start with the Ramping Mini-Calc. From the screen shot above you can see I’ve set up an aggressive machining scenario in 6061 aluminum. I’ve got a 1/2″ 3-flute TiAlN Endmill selected and it’s a serrated “corncob” rougher to boot. I want to set up my CAM program to…

Thanks for the Survey Responses!

Feb 23, 2011   //   by   //   Blog  //  6 Comments

I’ve now gotten about 30 survey responses, which is enough to start looking for trends and doing research on some new articles of interest to the readership.
First, some observations about the overall tone and content of the responses:
I really appreciate the constructive view most have taken. With the Internet, and particularly when there is the opportunity to respond anonymously, sometimes you get a lot of hostile or very unconstructive feedback. Not here!
There is one major challenge, but it’s one I’ve known about for a long time–the readership is decidedly bi-modal. What I mean by that is that there is clearly a large group that wants articles that are more “high-end”, “professional”, or “advanced”. There is also a group that wants more “beginner”, “introduction”, “shopmade/homemade”, or “getting started.” I didn’t notice too much in between, and both groups are almost the same size in terms of feedback responses. That’s cool. As I said, I was already aware of it and think it’s very healthy that I don’t go off too far in one direction or the other. Accordingly, I will try hard to publish articles for both audiences.
One other observation–a few bemoan the articles and talk about…

Old Machines May Not Die, But They Need Some Creative Fixing Up

Feb 21, 2011   //   by Bob Warfield   //   Blog, Products  //  No Comments

Many a small machine shop business or talented home hobby shop is started with an older CNC machine. I can’t blame a small shop, let alone a home shop, for not wanting to take on the payments associated with a brand new CNC machine. Once the shop that bought the machine new has fully depreciated it, they may choose to unload it in favor of something that’s newer and performs better. Recent economic stimulus has allowed machines to be immediately written off, at least the first few hundred thousand dollars, which potentially brings more new machines into shops and makes more old ones available to the next step down in the food chain.  Now is a good time to be looking at the old machines, because there are a lot of them available.
Getting one of these older machines involves overcoming two distinct issues. First is the mechanical side. Are the ballscrews and ways good? What about the spindle bearings? These are pretty expensive to replace. Assuming the mechanical side is good, thoughts turn to the controller. Many a mechanically sound machine has been bought cheap because of a dead or flakey control. If you’ve got the skills to fit…

Interpolate or Twist Drill, Part Deaux – Making Holes, Not Pockets

Feb 16, 2011   //   by   //   Blog, Software, Techniques  //  4 Comments

In an earlier article, I wrote about the relative merits of twist drills and interpolating a hole with an endmill.   The focus of that article was on the initial hole needed to start pocketing.  This is classically done by helixing the endmill down to depth and then proceeding from there.  The question I wanted to explore was:
Although, profiles and pockets often begin with the need to get the endmill down to proper cutting depth. Given that you know how long a tool change takes on your CNC mill, how many such plunges do you think are required before you’d be better off to use a twist drill to do the initial plunge and then let the endmill interpolate off of that?
I include an Excel spreadsheet to help calculate the two scenarios in the article, but the bottom line was an example that showed that as soon as you had more than one such pocket-starter-hole to make, the twist drill came out ahead.  I also discussed how a number of machinists keep a 1″ or larger insertable drill in their toolchanger for just such occasions.  In fact, here’s a neat little video showing exactly that approach in the making…

G-Wizard’s New Thermal Expansion Calculator

Feb 12, 2011   //   by Bob Warfield   //   Blog, Software, Techniques  //  4 Comments

I was paging through new posts on Practical Machinist and came across a discussion of thermal expansion. Since it looked like something useful, and something I wanted to experiment with, I whipped up a Thermal Expansion Calculator for G-Wizard:

G-Wizard’s Thermal Expansion Calculator…
It’s pretty simple to use:
Select a material, and it will enter the Coefficient of Thermal Expansion for that material. Keep in mind the note at the bottom–it uses the average across many alloys. For more precision, look up the exact coefficient for your material and enter it. I’d wait to see what the average reveals and if its within a factor of 2x or so of worrying you, look up your exact material’s coefficient.
Next, pick a temperature unit system, Fahrenheit or Celsius. Enter your Reference and Target temperatures. The standard temperature for measurements is 20 degrees C, and if you push the “Std Ref Temp” button that is what you’ll get.
Lastly, enter a length and/or a radius.
Press Calculate and G-Wizard will tell you how much the temperature differential between the Reference and Target will move the material in length or radius.
Let’s consider a simple problem you might use the calculator for. Too…

Release 0.122 of G-Wizard Editor (Beta) is Available

Feb 11, 2011   //   by   //   Blog, Software  //  2 Comments

There are quite a few new goodies in this release. The big news is the ability to download predefined CNC Controller (e.g. “Post” parameters) from the CNCCookbook servers. Hopefully this will simplify startup for new users:

You can choose from a list of pre-defined CNC Controller profiles to initialize G-Wizard Editor’s “Post”…
So far there are just Fanuc and Mach3 controls with variations to cover lathe, mill, and Inch or Metric units.
There’s also a new “Tortoise” and “Hare” feature inspired by the low and high speed range indicators on older Bridgeport milling machines:
Just click the buttons to speed up or slow down the g-code simulator’s playback speed…
More details are available on the G-Wizard Editor release notes page. If you haven’t tried GWE, give it a play. It’s still in early to mid-Beta test, but coming along steadily. The best part is it’s free in Beta test!…

Progress on the Mill Enclosure

Feb 9, 2011   //   by Bob Warfield   //   Blog, CNC Projects  //  No Comments

Got a little progress on the mill enclosure:

The sides are all bolted together…
The sides are bolted together. The design allows the side or front panels to be individually removed for additional access to the mill. We got all 4 sides made and the brackets set up so it could be bolted together. Next step is to apply West Marine epoxy for water proofing. After that we will paint and then start mounting windows, door, and various bulkhead fittings to get coolant and electrical into and out of the enclosure.…

45 or 90 Degree Face Mill?

Feb 6, 2011   //   by   //   Blog, Techniques  //  5 Comments

Of course if you can afford it, it’s great to have both 45 and 90 degree facemills, but what are the pros and cons for each?
Both Sandvik and Kennametal will suggest the 45 degree face mill is a better bet for general purpose face-milling. Incidentally, this is the sort of thing that’s a perfect topic for CNCCookbook’s Machinist’s Search. Try searching “45 degree face mill” using Machinist’s Search in one window and Google in the other window.
The arguments given by these two for choosing the 45 are:
– Cutting forces are better balanced so that axial and radial forces are about even. Lowering the radial forces so they’re more balanced with axial can not only enhance the surface finish, it’s also kinder to your spindle bearings.
– Cut entry and exit are better behaved–less shock, less tendency to break out.
– The 45 degree cutting edge is better for demanding cuts.
– Better surface finish–the 45’s leave a noticeably nicer finish.
– The chip thinning effect is at work and leads to higher feed rates.
– The 45’s tend to have less tendency to chatter as well.
At one time, octagonal face mills were at war with the…

Toolholding in Collets: How to Avoid Tool Pullout

Feb 5, 2011   //   by Bob Warfield   //   Beginner, Blog, Techniques  //  No Comments

Tormach has published a great report on variables that influence the holding power of R8 collets. You can view the pdf file here.
They basically did a series of tests while changing various things to see how that affected the amount of force needed to pull a tool out of an R8 collet. One of the most damaging things to the holding power is the protective oil that cutters come coated in. Cleaning that oil off and torquing the drawbar to 40 ft lbs resulted in an increase in holding power from 1300 lb to 3600lbs–big improvement!
The difference on a clean and dry shank based on drawbar torque from 20 ft lb to 40 ft lb was an increase from 1850 lb to 3600 lb. It’s worth it to drag out your torque wrench and “calibrate” your arm for what 40 ft lbs feels like.
They performed a number of other tests, but at the very least, keeping that tool shank clean and dry coupled with proper torque should be your starting point.
I’ve also seen figures on the proper torque for ER collets, and these are often much higher than machinists assume. See my article, “Getting the Best…

Introducing CNCCookbook’s Machinist’s Search

Feb 1, 2011   //   by   //   Blog, Software  //  No Comments

Have you noticed there is more and more spam showing up every day in Google’s search results? When I’m researching topics for CNCCookbook, I wind up going through at least 10 and more often 20 pages of search results before I’m sure I’ve got all the good dope. Along the way to creating a thousand pages or so of content here, I noticed many of the same sites would crop up again and again in my search results. They were like old friends, because I knew they had reliable information.
So I gravitated to those search results. It reached a point where it was often more important to look at which site the result led to than the little blurb Google gives about what you’ll find there. Like you, I don’t have time to waste, so I created a Google Custom Search Engine especially for machinists. You can access it via the link to the left or here.
What’s a Custom Search Engine? It’s a tool that Google provides that lets you emphasizes trusted sites over the normal Google search results. You still get the normal results too, it’s just that results with a good match from the trusted sites…

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