Messages

911

General Mach Discussion / Re: Supplier of small quantities of Titanium and machining recommendations

« on: January 14, 2010, 04:36:25 AM »

Well, now that the application is know, I can see the need for Titanium. Ferric Chloride is child's play compared to CBT (Caustic Burrito Turd) . . . . LOL!! In fact, titanium's resistance to CBT pitting indicates that the entire seat should be made from that material. CBT can adhere to wood and then contaminate any subsequent contact . . . 

OK, seriously, titanium is an excellent choice for a toilet seat hinge with only one small concern . . . . the application is in an environment where the presence of methane gas could be ignited by a cigarette and in turn catch the hinges on fire which would then burn a hole in your ass . .  ROTFLMAO!!!!!


Titanium toilet seat hinges . . OMG . . . what next . . . too funny.

912

General Mach Discussion / Re: Supplier of small quantities of Titanium and machining recommendations

« on: January 13, 2010, 04:50:06 AM »

simpson36, 316 is not all that chemical-resistant.  Common ferric chloride (available at any Radio Shack or Radiospares, depending on where you live and used to etch printed circuit boards) will laugh in the face of 316.

And in the biotechnology instrumentation industry, we went from 316 (even passivated or electropolished) to titanium two decades ago.  Now all PEEK and ceramic and other non-metals in the liquid path.

Randy

Ferric chlodide does not come in titanium bottles  . .  probably because there are cheaper alternatives.

316 is the standard in petro chem. Beyond that are the nickel alloys. Titanium is 'bio-compatible' and considering that instruments tend to use tiny parts, and that 'bio' is just another way of saying 'cost-is-no-object', it is not surprising that any bio-industry would use titanium. Titanium is used for dental parts and bone replacments too, not for chemical resistance or strength, but because it is 'bio-compatible'.

Titanium is not resistant to 'common' chemicals like sulfuric acid, which is used in anodizing, which is a 'hobby' activity. Not too many hobby level bio instruments or bone replacements being made with converted asian CNC machines, but lots of hobby anodizing rigs are in use.

However, pointing out specific chemicals that attack specific metals is academic when we do not know what chemical the OP is concerned about. Titanium is nearly 10 times the cost of 316 and comes with some hazards relative to machining it, so it seems prudent to know if is needed before taking that plunge, methinks. If he is building a ferric chloride pump, then he's on the right track, although I have heard of success using plastic aquarium pumps, which may be slightly less expensive.  

Titanium has good corrosion resistance to some chemicals, no doubt, but so do other less expensive materials. Titanim is used for primarily for its strength to weight ratio, being about twice as strong as 7075 (and 10 times the cost). With the notable exception of 'bio-compatible' applications, I would be surprised ot see titanium specified for chemical resistance over cheaper alternatives if strength and weight were not primary requirements.

And incidentally, www.onlinemetals.com has titanium in small quantities.

913

General Mach Discussion / Re: Supplier of small quantities of Titanium and machining recommendations

« on: January 12, 2010, 06:12:35 PM »

Titanium is not typically used for chemical resistance.

You might do better looking at stainless or the nickel alloys like Monel and Inconel.

Regular 316 SS is pretty much immune to about everything. Horrible to machine, though. What chemical are you resisting?

914

General Mach Discussion / Re: It's Alive!! It's Alive!!! (Insert Maniacal Laughter Here...)

« on: December 16, 2009, 11:19:32 AM »

Nice job, Ray. Much better than powering the rack and pinion drive which I have seen many tmes.

I'm noticing the seals on the ballscrew. What ball screw did you use?

915

General Mach Discussion / Re: Router heads

« on: December 16, 2009, 10:46:19 AM »

I have only cut a little bit of polycarb, so I don't know if it has similar characteristics to acrylic relative to killing bearings.

My guess is that the dust got into the bearings. You mat find that replacing the bearings with quality sealed bearings will solve the problem and increase the accuracy of the spindle as well.

If you are able, it would be a good idea to fit a 'slinger' on the nose of the spindle between the collet and the bearing as well.

I get most of my miniature bearings from BocaBearing. They have a non-contact seal that they call 'ultraseal' which I have used in RC helicopters with good success. There is no machine on the planet that destroys bearings faster than an RC helicopter,  so I would imagine they are a candidate for a high speed spindle motor. They have them in ceramic, but I don't know if they are available in ABEC3.

I replaced both the spindle and motor bearingd in my X2 with SKF 'precision plus' series. These are very nice 'middle of the road' bearings and are quiet, accurate and reasonably priced. I would categorize them as entry level commercial or high end hobby. Pay attention to the recommended max RPM  . . the limitation is normally imposed by the seal material.

NOTE: I am providing only information and not an endorsement or recommendation.

916

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: December 16, 2009, 10:24:09 AM »

Photointeruptors come in a lot of different flavors, some costing under US$ 1.00
Some have lenses over the LED and some do not. Some have wires attached and some have only bare pins. Some have polycarb housings and some use much cheaper plastic. Some are rated for vibration and some not . .  etc. etc.

In order, I have had lots of false signals from stray light and dust with the un-lensed parts, pins break off very easily on the parts with bare pins sticking out (in fairness, these are meant to be mounted on a PCB, not have wires hanging off them), plastic housings that dissolve seemingly in anything except distilled water, and finally, some just litterally fall apart. The 4th axis was the 'acid test' that killed a number of these parts, some of which were actually working fine as homing switches.

After the above experience with various recommended products, I have settled on the following rather expensive unit US$ 7.25 approx. It has wire leads, lenses covering the optics (to keep out dust and swarf), an indestructible polycarbonate housing that can bend a .060 aluminum tab that gets out of line and hits it, and can tolerate vibration.

It is a Honeywell model HOA 1887-012

I now have these on all of my machine axis and also on the 4th axis and they will be used on the commercial verison of the 4th axis as well. You simply need a 100 to 150 ohm resistor on the 5V that feeds the LED (red wire) You can use 5V or up to 30V for the trigger side. For example if  you use 5V from a BOB, you can daisy chain 3 of these and still have 3.5V return to the BOB. I have a little "Remote LED driver board" to boost signals, but it has not been necessary to use with these Honeywell interrupters and the Homann designs BOB.

917

General Mach Discussion / Re: Whose Fault Is ThIs?

« on: December 08, 2009, 01:54:11 PM »

As I kicked up the speed and accell higher and higher I got into an area where simultaneous slamming of all the motors at once started to cause occasional faults.

After clearing it with the drive maker, I installed big caps directly across the power terminals on each drive.

Not a single problem since.

918

General Mach Discussion / Re: What motor size and driver should I use

« on: December 07, 2009, 05:47:45 PM »

You did not mention voltage, so assuming you are OK with that spec, then it is down to amps. From all of my research and also proved out in my own testing and experience, I can not reccommend anyone use the 'continuous' rating on a servo motor as the basis for sizing servo drives for a machine tool.

The 'continuous' rating is exactly that; the limit of heat dissipation if the motor is producing full power continuously. Unless you are powering a conveyor belt, fan, agitator, vibrator, or some other industrial machine that is truly continuous, you can pretty much ignore that figure. On a mill or similar machine, 'normal' operation is anything but continuous. Repeated momentary peaks (accell/decell) with plenty of 'rest' (running at feedrate) in between is the norm. My assessment in a nutshell is this: consider only the peak. if you have a 50A peak motor and you run it with  Gecko, then what you end up with is a 20A motor. If you run the same 50A peak motor with a Dugong, then for practical purposes, you have a 35A motor. You will only have a 50A motor if you run it with a 50A drive.  

To answer you question directly, yes a Dugong would 'work' (provided the voltage is within spec), but it would limit the available peak amps to 35 and your motors are thirstier than that. The motors will likely run fine, but you will not get the acceleration they are capable of, so you would need to realistically assess your needs in that regard. There is no rule stating that just because you have motors capable of pulling anchor bolts out of the floor, that you have to use all of that power.  At least one poster here has 38A motors running off 20A Geckos and seems satisfied with the setup. HomeshopCNC was mentioned and they have a scope trace puiblished on their site clearly showing the Gecko shutting down the party at 20A, thereby loosing half of the motors performance. I am not saying this is neccessarly a bad thing, but it is a fact to be aware of and consider in your thinking. The performace at 20A might be fine for some applications. Similarly, 35A performance of the Dugong may be acceptable with your big motors, but you will not get the max out of the motors.

One would imagine the peak on your motors is far above the capabilities of any of the 'entry level' drives (including the Dugong) at this price point. Drives that would get the attention of your big motors would be far more expensive, so you have cost factor to weight. My advice is to be realistic in your expectations. If you make an informed decision to sacrifice some performance to save many hundred of dollars on the drives, and your application will perform acceptably without the max acceleration your motors are capable of, then you will have done a good job of selecting drives, IMO.

919

General Mach Discussion / Re: Whose Fault Is ThIs?

« on: December 02, 2009, 03:04:02 PM »

Just to comment a bit further, I've been noodling over why the problem went away for me, and what I assume is that I probably still have the problem with the A axis, but since I went to servo motors and then better servo drives, the issue has not been able to manifest because the motors get a little behind during the 'instant' accell,  but catch up within a tiny amount of movement, and most likely before the cutting tool touches the workpiece, so there is no practical effect.

If I recall correctly, I read somewhere that you are using Gecko drives. They have only a tiny error allowance and not much power (for a big motor), so they are unable to tolerate the error created by the slammed motor.


Be nice to have it fixed in any case . . . .

While I have your attention, Ray, let me repeat my appreciation for the great manual you have produced. Only used it a couple times, but even then it has saved me a lot of time and hassle.

920

General Mach Discussion / Re: acceleration

« on: December 02, 2009, 08:06:34 AM »

The effect of acceleration is not trivial.

Depending on what you mean by 'accuracy', acceleration has a huge effect if you are running high feedrates.

If by 'accuracy' you mean 'repeatability', which is actually what was discussed here, then it has little or no effect unless as has been mentioned, you push steppers too far and they start to miss steps. Missed steps are audible only if there are many in a row. One or two missed steps here and there cannot be detected by sound, but can add up to a big problem.

If by 'accuracy' you mean the machines ability to hold a tolerance, then again, acceleration cannot reduce backlash and cannot make the machine more rigid.

However, if you define 'accuracy' as how close the machine can follow a profile, then acceleration is king. High speed without corresponding high accelerations leave rounded corners and other anomalies. The effect is exactly like a race car needing to open up their line in order to make it around a tight curve.