Machining Aluminum #122 - Sydney, Australia

[Fox]

@Ken

You're calling me fat AND stupid ?

@Bruce

Do what you want, above 4:1 does not makes sense, I agree with Ken, anything below is based on your personal preferences and specs.

You can see how my 4:1 looks here: http://mechmate.com/forums/showthrea...&postcount=239

I put the spacers between the plate in such a way that one can encase the gearbox with 3 mm transparent polycarbonate strip ( to be cut on mm) ,to stop curious fingers, long hair etc.

[KenC]

Originally Posted by Fox

@Ken

You're calling me fat AND stupid ?

@Fox
Take it as a complement
Fat is the sign of prosperity
Stupid makes top politicians

For many, enuf is not enough... doubling the res is all it required to solve the chatter issue, but people just keep pushing into diminishing results with unthinkable complexity...

Jokes aside, if not for your effort, we won't know how ugly 4:1 ended up looking

[Fox]

You're always expecting to sand your edges you tell me ... even with an reduction you get chatter ?
Are you actually running reductions on yours ?
I'm just lazy and I've built a CNC to do work for me ... not to create extra work
Sure ... if you need to paint it really nice, you will have to sand it after sealing the edges cause the cut fibers will raise.
But I see no reason to scare Bruce he has to accept chatter with a beltdrive doing his curves ( and proper speeds and feeds and bits ).
Without beltdrive some chatter is unavoidable I think.
All this talking about an MM.


anyhow... Have a nice weekend to you all ! I'm off building my dust extraction.

[Tom Ayres]

I have 3.6:1 belt reduction, it produces a small amount of chatter with a 30t pinion, but a hell-of-a-lot less than direct drive with a 24t pinion, still enough to sand if I want it right. Regardless, wood will always require some kind of touch-up, period.

[racedirector]

This image is from another closed forum and this piece was produced on one of the old machines that I used to have. This is straight off the machine, no sanding. Now I must admit mine never produced this good hence my building a MM to improve things, based purely on pictures and videos I see here.

If I can get this kind of cut from 3:1 reduction boxes I will be a happy man.

[pblackburn]

As one of the those here that have a higher belt ratio (7.22:1) on 3 of my drives and a 4:1 on my Z axis, a 4:1 will render a fine cut quality. I only opted for the same ratio of 7.2:1 because I was reusing the steppers from the gearboxes or else I would have opted for the 4:1. I can say and I will post the next time I cut mdf but I do get an excellent cut on radius and rounded corners with minimal if any chatter. The benefit of a higher reduction does not justify the cost so I would not go above 4:1 unless you want to or you are required to do so.

[pblackburn]

This is the only piece I have right now and it is from when I was cutting out the templates for the cyclone build. The straight cut is from a saw when removing parts from the skeleton.

[clarson66]

We to went through the same, went from a MDF build with aluminium rails, skate bearings and leadscrew with great smooth curves to the MM direct drive. We found quite a bit of chatter but after playing with different bits and making sure we were cutting in the right direction (conventional not climb) it was quite good. I finally made up the 4:1 reduction from Surfcnc design and it's improved cutting curves quite a bit. Also depends on what sort of radius your cutting, try doing a small 100mm circle then cut a 1000mm circle. I've done some work for a sign writer and I have seen some of the stuff someone else has done a commercial machine and that still had some chatter.

[racedirector]

Thanks guys, I really do appreciate everything everyone is posting. Not trying to be a spoilt child throwing a tantrum. It just surprised me that my $6500 machine was worse at cutting than my $2500 machine. I'll shut up now and get on with addressing the issues I have.

[KenC]

For me, since need to do edge sanding, so while I'm at it, I give my rounds a goo rub & no more chatters... Direct drive 24T (Still ). Yes, Chris & Leon are right, bits do contribute a fair bit.

[racedirector]

Been doing a little tuning today, nothing cut yet though. Did find a loose grub screw on the X because I forgot tp Loctite them They are all done now so will have another bash at cutting something tomorrow inbetween watching the Bathurst 1000 on TV, my yearly ritual....

[ger21]

Originally Posted by racedirector

It just surprised me that my $6500 machine was worse at cutting than my $2500 machine.

In some cases, my $800 wood router cuts better than the $150,000 Morbidelli I use at work.

There are a lot more factors involved than just the gear ratio. Feedrates, tooling, chip load, spindle runout, tram, .... and others can play a factor in cut quality.

Also, you can get cuts that may not pass the eye test, but for all practical purposes are still perfectly fine.

[racedirector]

Originally Posted by ger21

Feedrates, tooling, chip load, spindle runout, tram, .... and others can play a factor in cut quality.

Being not very experienced in these I bought Bob Warfields speeds & feeds calculator and that helped me get things right with the feeds and speeds at least. I also made sure my Z tramming was spot on... or as spot on as ones eye is on a bubble level. I have yet to cut a pocket to see how good I got that. I also haven't measured my runout on my 2.2Kw spindle yet, one day when I replace my aging imperial dial indicator with a metric one

[pblackburn]

Bruce,
All spindles have runout, all cutters have an optimal running speed and each individual piece of material has an optimal feedrate. Even the same species of wood this can change. Most of the calculations will give you a safe starting point somewhere in the mid-range. You will have to make adjustments based on the piece you work with. As Ger says, there are many things that affect the end result and to me the end result is both the tool life and cut quality. Since most of my tooling purchases are a high quality tool, the life expectancy is very important to me. This may or may not be the case with you.

You have just completed the build. That does not mean you have completed fine tuning the machine. Even an OEM has to make adjustments to their machines (theirs are more minute because that have a locked down design). That is why most manufacturers require the model and serial number of the machine when you call for technical support because they need the settings for that machine. Here we form fit our machines to our own desires and choices. I have had to make many small upgrades to improve my Mechmate from what I originally started with as I learned what I should have done to meet my expectations. I opted for geared reduction of the spur gear type originally, the backlash of these greatly affected the cut quality of 3D work so I had to invest in making belt reduction drive. The best improvement I made. Direct drive will work fine for some but for others it will not. A safe bet from everything I read here is to opt for a 4:1 belt reduction upgrade later on as money is available. There is a trade off either way.

You have built a rock solid machine. That is a true statement. You must not take these little hiccups as you have not. This is a learning experience. You should not compare one machine to another either. Each has its strengths and weaknesses and the longer you run the Mechmate you will see what it has also.

[racedirector]

Pete, thanks for this grounding, very well put. I appreciate the time you took to do this.

You may have noted I have shut up about it now and have been knuckling down to doing little things to it. Nothing recut yet, still a few things to check and tune.

[Regnar]

Originally Posted by racedirector

I also made sure my Z tramming was spot on... or as spot on as ones eye is on a bubble level. I have yet to cut a pocket to see how good I got that.

Just wanted to make sure you have read this post.

http://mechmate.com/forums/showthrea...28&postcount=5

Makes squaring and tramming a breeze.

[racedirector]

Thanks for that Russell, missed that one. Currently gluing down my 2nd layer of MDF, will do the linked once that is dry.

[Regnar]

Glad it will help out. Just some other quick words of wisdom.


I mount a 24"x24" piece of MDF to the center of the table and use it for the reference table. I surface this piece with a .25 endmill with a 25% stepover. This reduces the size of the humps and I run it in both the X and Y direction. Use Raster and not a Pocket tool path. After that I use 2 drafting triangles and a wood dowel with a bent coat hanger in it. Works like a charm and longest hardest part is surfacing the small square.

[racedirector]

Thanks again Russell however I missed this being away all day. I have already surfaced the table - the first time wasn't thorough and the Z was infact off a little leaving little ridges in its wake. Spent another 30 mins adjusting things and gave it another whirl and this time no ridges and perfectly smooth. It took 2 more bites, one with zero off one of the low spots and the second .1" further down. Around 15 minutes each run with a 1 3/4" bit @ 13,500 RPM loping along at 500 ipm. The only downside of all this was no dust collection. I had my old shoe on to stop too much throwing out the side but I still have a massive cleanup to do tomorrow

THis is the very first time in any of my machines that I have had a perfectly flat surface with no signs of ridges whatsoever. Time now to cut my new dust shoe and router the dust pipe then its off to the races cutting things out!

[racedirector]

Very happy to today. I decided to cut a test version of the reduction boxes I will be using and the machine performed flawlessly. I am especially happy with my pockets in the MDF test pieces, they are perfectly flat with no sign of tool marks at all. This can only mean I have the Z tramming spot on.

Happiness however doesn't extend to the crap MDF I have been trying to cut, 6mm is definitely not 6mm - 2 sheets bought differed in size. Gotta love big box store Chinese crap.....NOT!

[pblackburn]

They sell the same low quality stuff in the US as well.

[racedirector]

Quick question....

Been cutting a bit lately and noticing this on some of the cut faces (see attached)

The chatter in the pic.... on the diagonal.... is this a consequence of direct drive or resolution - I am using 30T pinions direct drive.

Oh and 3mm bit, 80 ipm, 3mm depth of cut.

[pblackburn]

Does this appear on a straight cut? How many nodes are in the vector? May be a combination of things, resolution and cutter chatter. A little more information about the process would be very helpful for all to answer? Even the smallest mundane detail can sometimes lead to the answer.

[racedirector]

Straights are fine in both directions, actually damn nice - only non straights exhibit this. This particular piece has the following nodes on the curves.

I was suspecting vibrations from the material while cutting as well but the cuts are the same if the cutter is right next to a screw (I am cutting full 6mm sheets screwed to the spoilboard at around 300mm intervals)

Cutter has a 25mm stickout from the collet.

[Fox]

I'd say direct drive from my lazy chair, cause of the two motors (three actually) working in conjunction on the diagonal. Plus maybe some mechanical slop / backlash. Both will be non existing on straights an raise their ugly face on diagonals and circles etc.
Check all the usual culprits (everything properly tightened and meshing etc) for the mechanical part of above.

[danilom]

Convert those dots to Bezier curves, depending on the software option would be CURVE FIT VECTORS.

But the chatters looks like some other mechanical looseness (spindle holder, bearings, wheels) if not from direct drive or rough vectors. Do the smoothing nevertheless always.

[racedirector]

Thanks guys, lots of things to check. Will get onto all these things and see what happens

[pblackburn]

Also check if the gantry is getting racked somehow

[Tom Ayres]

I ran direct drive with 24t pinion for a while and it too had similar but smaller chatter. An effect of rack and pinion. My answer was belt reduction. Very faint chatter now but still there none-the-less. Already time for an upgrade

[racedirector]

Just cut some 12mm MDF with a 6.35mm downcut bit @ 90 ipm, 4mm DOC. Chatter was better in places but the same in others. Gentle curves were spotless. So deducing a) material under 12mm is tricky to cut nicely without some form of vacuum table and b) as Tom say, upgrade to the belt drives. I actually have everything for my drives except .5" flange bearings which are exceptionally hard to find in Aus.