This February CamInstructor.com hosted a virtual webinar event mostly dedicated to advanced MasterCAM programming.
They called it the Big Event.
I myself watched at least 2 streams. But since it was a whole day thing, only missed a few.
Luckily they published all the videos on their web site:
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Check it out before the link expires or they take it down!
Often times CNC programming tutorials only teach you how to create the tool-paths and not enough attention is paid on showing how to properly hold parts being machined.
At the same time efficient workholding is an art in it self and mastering it could drastically improve shop productivity and accuracy.
Without further ado let's jump into the workflow.
We would have to look at the drawing, tolerances and the CAD model to develop the machining strategy.
This particular part has tight (+/- 0.001) tolerances between the features located on the top and the bottom sides. In addition to that it has a 2.5 degree draft angle on external walls.
Thus I decided to not use the soft jaws approach and machine it in a fixture. Soft jaws are generally OK for tolerances down to +/-0.001" but because of the draft angle the part would always want to pop out of the jaws.
Because it is: 1 - easiest to hold and locate on to and 2 - has the least number of critical features that may become out of tolerance after the bulk of material is removed:
While the whole batch is being machined on one side I design and program the fixture and the other side of the part.
In this case fixture is simply a pocket with a threaded hole and a special jaw with threaded holes that I use for other fixtures - it is used to temporarily hold the part for machining the clamping area on the part it self.
Temporarily clamp it down using a toe clamp and machine the finished face that will be used to hold the part down for the rest of machining
Do not forget to change your Z Offset for the new height!
Do not forget to remove the temporary toe-clamp or BAD things will happen!
Machine the rest of the part.
That's it! The first complete part is machined and should be sent to QC for sign-off.
The main difficulty that caused this multi-step setup was the need for accurate positioning between features on both sides of the part. And the fact that the external walls had a draft angle that made it impossible to use soft jaws.
Let me know in the comments if you have any thoughts or if you would do it differently ;)
Cheers!
2. First Op: Before
2. First Op. After
3. Machined Fixture
4. Second Op: Bearing Seat
5. Third Op: Finished Part
I came across a very educational post on Practical Machinist.
The topic-starter used over-aggressive speeds and feeds for his tiny BT30-taper machine and the retention knob (a.k.a Pull Stud) snapped causing the holder to drop lower, disengage from drive lugs and mess up the spindle bore in the process.
Just in case you don't know. Retention Knob looks like this and is used to pull the tool holder in to the spindle bore, thus holding it in place:
(Retention knob is the detail on the right)
This whole article is to remind everyone the importance of proper tool holder and retention knob maintenance.
Those are all the things I could think of at the moment.
Let me know if there is anything missing.
Have a safe and productive week!
We have many helpful articles over at HSMAdvisor Help portal. But beacuse of that very reason not many website visitors actually read any of them.
It is a pitty that most advanced users will never actually visit the help section, because they already know how to operate HSMAdvisor.
And this particular one, I believe, is too useful (I just updated it to include more info) for my customers and other machinists to keep it burried in some help section that few ever read.
This is a short Application Guide for use of different cutting tool materials and coatings.
Tool Materials and Coatings are listed from least preferable to most preferable.
(IE: line "Recommended tool materials: HSS, HSCobalt, Carbide, Diamond" means that HSS is the least preferable material and Diamond is the Most preferable one)
The following guidelines are mostly for milling operations, but, with some reservations, can be applied for turning and drilling as well.
Coating improves wear and temperature resistance of the cutting edge.
General rules of thumb:
Do you think this information is not complete or you need more?
Drop us a line.
See Contact Details for ways to reach us
Being a CNC Machinist/Programmer is sometimes more than simply creating a program and machining the actual part, often times it is about creating efficient and accurate fixturing.
In this little project:
I had to machine rectangular cut-outs and drill holes through an already-turned steel ring. Then I had to part each ring to 4 equal pieces.
There were about 100 such rings that worked out to 400 pieces in total.
After drilling holes on an indexer I had to machine a fixture to hold my part through 2 remaining set-ups.
First half of the fixture consists of the expanding mandrel:
The work-piece would be mounted on it like so. A hole on the side is used to properly position it:
The mounted part already has cut-outs machined in the first op on the same fixture.
After slightly tightening the screw, the second half of the fixture is installed. It keeps the 4 machined pieces in place after they are parted from each other:
Then the screw is tightened even more until I can no longer turn the top half of the fixture by hand.
Both the lower and the upper halves are machined to slide-fit to the work-piece, so that when the mandrel expands it clamps the work-piece against the upper half.
By the marks on the fixture you can see where machining was taking place.
And yes, I accidentally machined my fixture by crashing a small end mill into it - MasterCAM did some weird stuff with rotating my toolpaths and messed up the g-code.
Unfortunately I forgot to snap a picture of the finished part.
But I think it is clear from the sketch how it should have looked.
This is one of those cases when coming up with a fixture takes more time and effort than programming and machining the part itself.
And its fun!
Cheers!
One of the most versatile ways of clamping irregular -shaped parts is with use of soft jaws.
In this one I had to machine a triangular-shaped part from two sides.
It is going to be some sort of a part holding jaw for a robot.
So step one: Machine one side of the part in vise. hold on to 1/8" of stock. So make sure to cut your part on a bandsaw oversize.
Step Two: Bolt soft jaws to your vise and machine a pocket using outside contour of your part.
Be sure to relieve corners.
Step three: Clamp your part in the soft jaws and machine the second side of your part.
One important thing to consider is: this method is not very accurate. depending on the size and a shape of your part you may be able to hold it within 0.001" though.
See attached photos of the steps below.
2. Machine pocket in soft jaws
3. Clamp the part
4. Machine the second side
Recently I had to machine a few pieces after turning.
Because the very top of the part was supposed to be machined off, I could not clamp through the central hole like I often do.
Decided to quickly turn an expandable washer out of aluminum and a plastic spacer that would collapse a little bit under clamping pressure and allow the part to sit firmly against the base of the fixture.
I liked this method so much I am going to do the same next time I have similar part to make.
See pics below.
Later on i will try to post some more pictures of other setups I did.
Fixture, spacer, expandable washer, FH screw
Workpiece mounted on
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There is more than one way to skin a cat! Previously i have showed how to machine multiple pieces out of a flat plate holding only on to 0.010" thick material on the outside of the part. (here) But there is more than one way to do it. Sometimes your part is so hard to hold, that using tabs or skin is the best, or even the only way of machining something. Very often, working in prototyping, I have to make only one single part and designing and producing special fixturing is also not feasible. |
Here is how you can easily machine a difficult-to-hold part from both sides without using a separate fixture:
Setup: Put or part in vise. Make sure to square off at least two sides contacting the jaws for accurate positioning and minimum distortion.
Program part normally. Perform as many operations on the first side as possible.
When machining outside profile, machine to the exact depth of your part.
Here is how your part might look after completing the first OP:
(Sorry, a bit out of focus)
Make sure you finish the outside flanges of your part good if you plan to use them to sit part on parallels, like i do in the next operation!
After machining one side we would normally set up a fixture to hold the part from the inside hole, then re-clamp it and machine the inside hole features. This requires quite a lot of planning and also makes you stop mid-operation to re-clamp the part.
Never mind having to worry about avoiding clamps and bolts!
What i did instead is i flipped part over in vise and put it down on parallels:
Next i machined as much as possible from the back side while i still had enough meat to hold the part securely.
After machining critical features i programmed a pocked using outside profile of the part as my boundary thus finishing the back face of the part. I made sure i kept at least 0.003" in xy away per side from my finished size:
That't it.
After a few knocks on the scrap flanges, the inside part simply falls off!
Only minor deburring is required to remove the sharp edges.
Here is the finished part.
Shrink fit holders and extensions often come with a big through hole.
Its primary use is to allow the shank be knoked out from he back should the tool ever snap off. It is also used to supply coolant for CTS machines.
Unfortunately said hole affects rigidity of the holder making it more likely to chatter leaving bad surface finish and badly affecting tool life.
There is however an old trick to prevent or minimize the chatter.
All you have to do is pack that hole with some thick grease.
Don't forget to cap off the oppening so that grease does not escape when the tool is spinning.
Here are several photos of surface finish before and after grease application. All cutting parameters were exactly the same in both cases.
after. surface finish is ideal
tool in extension holder
showing capped hole
I recently had to machine an aluminum mold cavity.
7 inches deep. With 5 degree wall draft and a 60 thou radius going all the way down. Roughing was not an issue, but for semi-finishing and finishing i had to manufacture these two extension holders.
Both tools have runout of less than 0.001
The one for bigger 3/8 tapered ballnose cutter is shrink fit- i mounted it using torch.
The smaller tool is a 3/32 tapered ballnose cutter from Harvey Tool.
I could not bore to correct size, and had to ream right on.
The tool is mounted with a set-screw from both sides to prevent deflection caused by unequal clamping pressure.
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