co cr milling with vhf k5 ???

[dr.swapnil pande (MDS)]

any one has experience about co cr milling with vhf k5 ??? and does metal milling hampers machine life ????

 

[brayks]

OK, fair warning, here comes one of my long-winded posts…

First let me mention that I am

1. A distributor of a competitive product and
2. I have no personal experience with this machine.

However I can provide some observations and opinions based on my approximately 40 years of CNC/CAD/CAM experience (which includes repair of CNC machines, machinist, technical support, sales, software development and executive management) and reviewing machine/ spindle spec sheets, images, videos etc.

At first glance the K5 appears to tick a lot of the boxes necessary to consider this a decent machine. I really can’t speak to the value as I am missing a few bits of key information, including drive system (is it an open-loop, step motor system or closed-loop servo drive system) and price.

The boxes “ticked” include:

• · Ball screws (although unknown if there is preload)
• · Aluminum casting (although it appears only the bed)
• · Constant torque spindle
• · Linear guides
• · Harmonic drive rotary

I do however have major concerns with this machine relative to your post on machining CoCr.

First it is important to understand two very key concepts about machine tools and machining (there are more but let’s just concentrate on the two biggies). They are:

1. Heat and vibration are the absolute enemy and must be eliminated at every possible opportunity in machine construction, tooling and fixturing.
2. The spindle is really the heart of the machine and in many cases the limiting factor in its effectiveness for a given application.

The spindle appears to provide by what appears to be a smaller German manufacturer by the name of Dreiling-Maschinenbau. Concerns lie in spindle repair time and obtaining replacement parts (or spindles) when needed both in terms of time and cost.

Further, I do not believe this to be a machine to machine any steel, let alone the very hard chrome-alloys.

In my mind, by far the biggest limitation of this machine is the spindle.

I was unable to find any specific technical information on this spindle other than what was available on the VHF website. However from what they did publish and my personal experience with CNC machines, I can pretty much figure out what we need to know…and it is NOT spindle power in terms of watts. What we ARE concerned about is torque.

This particular spindle (SFK300P) is said to have a maximum speed of 60,000 rpm. with a max power output of 500 watts (we could care less about max power). More importantly (for terms of determining torque) it has an S1 (continuous duty) rating of 300 watts… and yes this light power for cutting metal.

Now on to torque which is the real key. Since no torque numbers are available I have to extrapolate based on what I know about his motor, what I know about spindle motors and what other manufacturers specifications are for their “like” motors.

So, this motor is a “synchronous” motor also known as a DC motor which is good here because these motors deliver pretty constant torque throughout their rpm range.

A very similar DC motor made by what I consider to be one of the best spindle motors for dental applications (yes even better than the much lauded Jaeger) has a max power of 650 watts and an S1 continuous rating of 400 watts. Max rpm is 80,000.

Although the Sycotec is more powerful and not exactly the same at the SFK300P, they are close enough to compare for metal cutting applications (both of which I would not even consider). Enough about power, back to torque.

The Sycotec (while being potentially more powerful),only generates 6Ncm of torque (continuous) with a maximum torque rating of 8Ncm. Not a whole lot of torque considering abutment screws typically require 25-35Ncm and milling screws about 10Ncm.

To give you a frame of reference, our Versamill 5X-200 has a 3.0Kw DC spindle that generates 40Ncm at about 30,000 r.p.m. Our machining templates require around 24Ncm for titanium abutments (produced on-average in under 20 minutes) and around 30Ncm for CoCr overdentures (produced on-average in about 75 minutes or so).

So I guess, if you HAD to, you could machine CoCr but you would have to slow the machining process way down in terms of spindle speed, depth and width of cut, feed rates, etc.. Doing so would not only affect cycle-time but also result in decreased tool-life and lower quality restorations.

Another big problem and limiting factor (another deal-killer) is the 3.0mm tool shank.

This causes a significant amount of tool deflection in the cutting process. Think of this regarding small diameter tools:

• · Smaller tool shank diameters mean less tool rigidity and longer stick-out lengths.
• · Rigidity decreases by a power of 3 relative length.
• · Rigidity decreases by a power of 4 relative to diameter.
• · Subject too significant tool deflection.
• · Creates chatter, excess tool wear, reduced accuracy and poor surface finishes

Just take a look at the tool stick-out in the images attached. I have to tell you I personally would never attempt such extreme diameter to length ratios in my tooling, especially for metal. The “whip” or deformation is "ridicumus". That tool would be slamming the material and it would be like hitting a gong, destroying the tool coating/cutting edges and leaving some nasty marks on the restoration (see image). You might be able to slow it down to help minimize the problem but I wouldn’t expect too much. Tool wear, tool breakage, bad finishes and severe accuracy problems would quickly become a problem far sooner than related machine issues- and that assumes the most rigid of rotary axes and fixturing, which by the pictures and videos I see are a bit suspect themselves (The K5 fixture, unlike the Versamill is only held on one side).

Take a look at the images attached from VHF'sown website where you can actually see the chatter in the metal puck. Check the other images and the video from the link below: you SEE the deformation in the cutting tool - and that’s only cutting zirconia and PMMA!

Now, will you hurt the machine if you produce CoCr restorations? Well who knows? Maybe, but likely not for periodic use. Keep in mind machine builders (well most anyway) pretty much utilize components and construction techniques that work together for an intended purpose, basically picking components and utilizing assembly/manufacturing techniques to keep costs down to reach their application, market price and profitability objectives.

You may run the risk of pushing the machine to the limit to where you would get early failure on some components… or maybe not. I for one would be pretty concerned about that lower power spindle, hurting it and possibly dealing with the replacement/repair issues that could rear their ugly head.

Just my 500 cents

Steve

Watch the YouTube video you can see the tool flex the comparatively free-cutting PMMA.

 

[zero_zero]

I really can’t speak to the value as I am missing a few bits of key information, including drive system (is it an open-loop, step motor system or closed-loop servo drive system) and price.

Nema 17 steppers, open loop, 0.5Nm holding torque...costs about $40...

 

[cadfan]

Why does every "idiot" think you can milll cocr because VHF tells . This is the only company i know whose telling they can on such mill in the long run sorry they are idiots to tell such thing ask Resellers to give you a guaranty for 4 years whithout cnc controller or stepper or ballscrew change and a few bucks repair and a few bucks outsourced money while repair . Yes it can but how long ?? double idiots sorry i know A FEW OFF THEM:

How would you mill a 40 mm blank with a 40 mm tool total lenght with only with 20 mm exemption storytellers sorry.


@ zerozero i paid 70 euro for one so 40 is realistic for high volume the only cool thing is the casted frame

 

[zero_zero]

@ zerozero i paid 70 euro for one so 40 is realistic for high volume the only cool thing is the casted frame

This is from the manufacturers North American webstore...high volume should be cheaper

 

[brayks]

now don't get me started...
Absolutely agree. I fight with this every day.
"Well so-and-so from bla-bla said thet could do it too, and their much cheaper"
Exactly!
So I'm the bad guy because I'm trying to be truthful educate. Problem is many don't want to listen and I'm the liar or the rip-off dude trying to extort more of their had earned cash.
Errrr...
OK, I feel a little better now.

 

[brayks]

Nema 17 steppers, open loop, 0.5Nm holding torque...costs about $40...
View attachment 25410
View attachment 25411

Thanks zero.
Seriously?
Honestly, our Versamill 5XS blows this one out of the water and it's under $30K with CAM, training, starter tooling and material package!

 

[cadfan]

I am the bad guy because i fight against these bull**** tellers lets give you 3 years guarantee on steppers ,axis and cnc controller not the spindle it can go down on a few reasons but the rest can be constructed for your propose . If anybody milled cocr on their 4K2 as they told evberybody they where non existing today. Dont trust idiots!!!!! it works but on your risk.If you realy what to mill co cr in the long run whithout 200 watt servos min and 12 mm (better16 mm)screwballs you die sooner or later

Steve versus brayks mill is equal or better but hes not an idot to allow you to mill co cr.

 

[JMN]

It's easier to fool someone than convince them they've been fooled.

You can pull a 40ft trailer with a Honda Civic. But neither will last long.

 

[grantoz]

ive tried milling cocr on a loner vhf mill it wasnt great a couple of years back very patchy finish, of course it will shorten the life of the mill its really hard cocr.

 

[brayks]

It's easier to fool someone than convince them they've been fooled.

So, so true. But I'm not giving up.

 

[JMN]

So, so true. But I'm not giving up.

Of course not. You're in the dental tech world where the impossible is accomplished daily.
(and most all have had an infarction in our 'know when to give up' area.)

 

[Affinity]

who wants non-precious metal ? We dont make fire with sticks anymore.

 

[Sevan P]

Just posted to the fb vhf group, don't know if you guys can see it or not.

https://www.facebook.com/groups/1569994006578983/permalink/1899226503655730/

Sent from my SM-G920V using Tapatalk

 

[brayks]

Thanks Sevan,
These images pretty much illustrate my point. Yes it can be done. However the problems associated with the machines construction (as related to machining metal) are displayed in the quality of the resultant abutment. I am curious has to how long it took to complete this abutment.

It's tough to analyze it thoroughly as the images are of low resolution and taken at a small zoom scale. However there are a few obvious signs that, as suspected the machine's rigidity, ability to absorb vibration, spindle and drive system are likely not up to the task in the long run.

The images posted clearly shows these signs. Particularly in the attached image where you can see the results of chatter, axis misalignment and likely stall. These can be seen in in margin/collar and post.areas. I suspect that it is possible the CAM software and machining templates also played a role.


The images below will give you an idea of what the Versamill produces.

Please do not misunderstand my intent here. It is not my intent to speak ill of the competition or of the work you have presented.

My intent is to give forum members an idea of just how important machine construction and software are and what is possible from a machine constructed with elements specifically designed for rigidity, to absorb vibration and to dissipate heat - all elements required for the long term reliable and effective machining of metal restorations.

Of course CAM software and machining templates are of great importance as well. But that's a different subject...

 

[Sevan P]

I agree, just saying the OP asked if it could be done and I just showed him. 5x200 with a 3.0KW spindle will hands down handle Ti like it was Zr. Those mills are built for Ti and CrCo would be overkill to cut wax, pmma and Zr.

 

[brayks]

I agree, just saying the OP asked if it could be done and I just showed him. 5x200 with a 3.0KW spindle will hands down handle Ti like it was Zr. Those mills are built for Ti and CrCo would be overkill to cut wax, pmma and Zr.

Hey Sevan,
That's what I thought.
Yeah, typically true for the lab not needing metal cutting capability, depending of course on quality standards, production rates, reliability requirements, flexibility and how long you wanted the machine to last.

For example, Argen has 60+ 5x200 machines, (the majority of which machine "soft" materials),reliably running very close to 24 hours per day with original spindles- some with over 140,000 hours. These machines are smoking (high rpm/high feed)! Impossible to get that kind of performance out of a machine that isn't built to the 5X200's specifications. Goodness knows they tried.

For the smaller labs, without the hard metal requirements, the 5XS is likely more appropriate. It is built like a tank as well, but instead of a cast aluminum-alloy frame, it has a complete aluminum fabricated frame. It also has ball screws & linear ways with pre-load, massive rotary reduction gear, 500w spindle, built in machine control and heavy duty stand. At $30K for machine, CAM, training, tooling & material starter packages, it completely out class's and out performs comparable priced "appliances" or machines costing thousands of dollars more.

Sorry, got carried away there... end of commercial.

 

[Sevan P]

Your absolutely right, Argen had 28 dwx-50 huffing and puffing 24/7 surprised they lasted as long as they did. 5x200 is a superior mill for a good price as well.

 

[2thm8kr]

reliably running very close to 24 hours per day with original spindles- some with over 140,000 hours.

That is nearly 16 years on original spindle?? Are they milling butter?

 

[brayks]

That is nearly 16 years on original spindle?? Are they milling butter?

... and in a time machine. LOL. Sorry for the typo...14,000