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-   -   Experimenting with options for vacuum clamping - Taibao, Taiwan (http://www.mechmate.com/forums/showthread.php?t=849)

DMS Wed 29 October 2008 21:44

David,

What bit are you using for Alu ?
I 've tried various bits, feed rate, router speed, oil, but still not satisfactory cutting.

Thanks,

J.R. Hatcher Thu 30 October 2008 05:23

I have not tried these parameters. I watched a video and it was cutting perfect so I ask for this information. Here is what I was told. Hope this helps.

Cutter: 1 fulte, Belin 33060
Lubricant: None
RPM: 18,000
Feed Rate: 48 ipm
Cutting Depth: .020 per pass

Gerald D Thu 30 October 2008 08:18

Different types of alu cut completely differently. Some alu's are easdy to cut, others are nearly impossible. I don't have some names/specs over here at this PE airport. (Hennie, I'm watching you!) The lubrication/cooling of the bit is also critical.

CNCQuest Thu 30 October 2008 09:00

Hi David,

Nice MM built.

I have encountered the same kind of seizing and whining noise when doing a continuous jog in my cnc mill. It was solved by reducing the velocity and acceleration in the motor tuning page.

Quote: "I've lowered my settings in mach to 15,000 pulses per min from 17,000 and that has helped and my acceleration setting is now at 550 vs 700."

Is that 15,000 pulses per min the velocity or should that be 15,000 mm per min? What kernel speed are you using? Try lowering your velocity by half and gradually slide it back up until it whines again. Then, back off by about 10 to 25% lower.

Can you give more technical info on the Chinese spindle?

Thanks and 謝謝,
WT

DMS Thu 30 October 2008 11:12

1 Attachment(s)
Thanks J.R, and Gerald,

I have tried on 3mm Alu sheet with as low as 50 mm/min and 15000-20000 rpm.
With end mill, drill,vbit, ball now, etching bit, carbide 2 flute etc with gummy results.:(
J.R. I could not find Belin 33060 on google. Only this post of Gerald on shopbot - http://www.talkshopbot.com/forum/mes...tml?1140534866

Are you talking of these bits? http://www.plasticsmag.com/ta.asp?aid=4152
Belin 33060 search returned nil on this site.
If not then a link may help.

David,

As WT mentioned "Seizure problem", Initially I've tried higher acceleration, and had same problem, with bit research I set to 3000 mm/min for x,y, A and 500 for z, which is comfortable speed for gear 7.2 and 36 teeth pinion. Kernel speed 25000.
I used this sheet http://www.mechmate.com/forums/attac...8&d=1207239352 for calculations but when I used speed given in this sheet (20,000) I had noise and stall. For this geared steppers this seems to be very high. I checked pdf of motor spec where I found permissible speed 250 rpm for pk296-sg7.2.

What I actually did - I did axis calibration in Mach with help of "set steps per unit. I found 125 against excel sheet of 127.324, I used this formula for calculation -

Speed per mm per minute = drive micro steps X motor steps per rev. X motor max.RPM / steps per mm

= 10 x 200 x 250 / 125 (actual)
= 4000
I set for lower side i.e. 3000

Now in your case, you have 20 teeth pinion so your speed comes to nearly 2200.
May be this is helpful. I have done this 3 months ago and it is working fine till now.
So guys correct me if I am wrong any where. (I am bit forgetful these days :D and my wife has long list of complaints about undone works.)

Thanks,

Gerald D Thu 30 October 2008 23:05

The alu cutting posts have been copied to a new thread, where some previous posts on the topic are being collected:

http://www.mechmate.com/forums/showthread.php?t=1020

liaoh75 Fri 09 January 2009 17:13

I've been very busy over the last few months. I run a language school in Taiwan and from October to December is a very busy time. Just a quick update on what's going on. I've taken apart the entire machine after satisfactory testing for a re-paint.

Gerald, I seldom spend much time on the main homepage but had a quick glance to find my build listed with a picture. I am honored you would place my build on your home page. I'll supply a better picture with appropriate Logo as soon as I finish the paint job. Thank you for providing the plans and thank you to all that helped on this fantastic journey. Thanks Team Mechmate!

Gerald D Fri 09 January 2009 20:11

Hi David. Good of you to call back in and let us know what's happening. Thanks.

domino11 Mon 07 September 2009 10:40

David,
Did you ever get your labels? You are really close to a serial number. :)

liaoh75 Tue 08 September 2009 10:34

Heath, Mechmate Logo has been on my Blue Beast for a good while. It has been very busy cutting away for quite some time now. We are finally moving to a Chinese Spindle after several bearing changes on the Porter Cable Router which held up surprisingly well. Some might find it interesting that the main reason for making the change is easier access to wider collet sizes available for an industry standard collet like the ER20. It is cheaper to buy a 3mm 0-flute solid carbide bit with a 3mm shank than a 3mm bit with a 6mm/.25 inch shank. We are going to keep the Porter Cable as a spare in case something happens to the Chinese Spindle.

I also have a two year old son and my better half that needs some of my time. I think I've been elgible for a serial number before the list broke double digits. However, I think I've just been so busy with the two growing businesses, I haven't made it a priority to get my serial number. After getting the spindle mounted, I will take pictures and post all the modifications with dust foot, replaced spider plate, and completed control console.

Thanks for the bump!

Charlie Tue 08 September 2009 11:32

Also make sure you set your steps per rotation. The 7.2s I believe are 1440 steps per rotation (0.25 step angle) not the 2000 that my Mach3 defaulted to. My motors ran so much better when this was set. If you have done this Great, but I didnt see it mentioned so I thought I better make sure.

domino11 Tue 08 September 2009 13:12

David,
Good to hear everything is going well. Look forward to your new posts when you have the time. I have two little ones as well, so I know what you mean on the time issue. :)

liaoh75 Wed 09 September 2009 22:17

Hi Charlie, thanks for the numbers, but believe my machine has already been set correctly but I'll double check!

Gerald D Thu 10 September 2009 00:20

Charlie, a typical stepper motor and gecko combination is 2000 steps per rev. Add a 7.2 gearbox to that motor and it becomes 14 400 steps per rev.

If one makes a mistake in this area during the Mach3 setup, it is immediately visible in the scale size of the parts you cut out........add a 7.2 gearbox and watch your parts get 7.2 times smaller! :)

Charlie Fri 11 September 2009 18:23

OMG what?
Well I need to figure this out then. Im looking into it right now but if you could post more info Ill take it. Maybe mine smoothed out because it was closer with ten steps at a time? See I had a rough spot in the rotation. It would come around then and make a little magnetic rumble. Ill try adding another zero. *embarrassed**
This is all still bench top work.
Charlie.

Gerald D Fri 11 September 2009 21:51

See Understanding & Selecting gear pinions - setting the steps per mm[inch]

Charlie Fri 11 September 2009 23:24

I have been looking at this for hours. I now have it set at 3055.777488 steps per "unit". I had a full step/micro step lesson to learn. I will study the link Gerald thank you. Most likely I still have errors. The rough spot in my motor went away from something else because I reverted back some settings but the rough spot didnt return. Who knows?..I have been having a blast messing with them and making them sing.
Charlie.

Edit: Read the thread you linked and I was glad to know that I managed to get my 3055.777488 number before I read it. I thought you should know Gerald :)

liaoh75 Fri 26 March 2010 10:31

7 Attachment(s)
It's been a good while since my last posting to my build log. I've been busy working on building a business around the machine and running my Language School. I've got a little more time now so I'm going to start working on catching you guys up that have been following my build.

I'm going to start putting together a vac hold down system with a target budget of $1500 total. Over the last several months I have been experimenting with a number of pumps. I've tried:

1) shop vacs (industrial - probably more robust than the revered Feins albet a bit more on the noisy side, but not too bad) They all seem to fall short in some way or another. Vac wasn't that great (6-8" Hg at best with no leaks) and air volume was marginal. Couldn't really hold parts very well. I setup a test bed for these experiments as I didn't want to commit to setting up vac plenum and sealing everything without deciding if it was finacially feasible to do this.

2) dust collectors 2hp and 12 hp These had tremendous air volume but gave about 2" Hg on the best test run. Cheap but completely out of the question.

3) Regerative Blowers. These actually would work if they were big enough. I tested a 7hp and 15hp unit and like the shop vacs, they didn't pull very much vac but was top dog when it came to air volume. The sales guy told me flat out not to use a regen blower for my application and suggested I look into roots blowers or oil filled vein pumps. He said that many have tried using regen blowers with marginal success.

4) roots blower. Here is where things started to get interesting. I found a vendor about a 1.5 hour drive from my location that sold referbished Japanese (hand-me-downs) I spoke to the owners for quite a while about the pros and cons of all the pumps he had on hand. I asked to test out his units with my experimental setup. He agreed and seemed quite confident that his 5 hp roots blower (2" port) would probably do the job. One week later, I showed up with my test board (4'x4' with routed out plenum and one hole in the middle (single zone). The bleeder was an import (Thailand) 1/4' run of the mill MDF board that was the same size as my experimental plenum. I had one metal ball valve with a vac gauge before the valve so I could see how much vac the pump delivered. I was quite surprised. After sorting out the plumbing, we fired up the 5hp roots blower. It was a noisy thing to be honest as the guy didn't put on the muffler for the test. The gauge jumped to about 17" Hg. I opened the valve to the plenum with bleeder only and the gauge fell to about 1" Hg. I started putting flat objects on the bleeder one at a time and slowly the gauge started to climb again. When the board was almost completely covered with pieces of board, the gauge leveled out at about 9". From reading on the shopbot forums, this seemed to be the magic number: 9". All the flat pieces adhered to the bleeder quite nicely and took a good amount of force to move them; Way more force than a 12mm (1/2") cutter would exert of a piece of board. I was blown away. Price: ~$800 U.S. dollars with a 1 year warranty

I then asked if I could try the next step up from the 5hp roots (2" in and out) to a 10hp version (3" in and out). Thats when I came to the realization that a $1500 competent vac hold down was possible. When he fired up the 10HP monster of a pump, the gauge instantly jumped to 23" Hg, I opened the valve with only the bleeder and still pulled 5" with nothing on the board. I put a 2' X 2' by 1/2" piece of acrylic on the board and couldn't budge it with two other people helping me. The rest of the bleeder was completely open. The vac gauge read 15" Hg. Price: ~$1000 US dollars with 1 year warranty. (This was the pump I ended up buying.)

We then moved to a final test with roots blowers which was a monster 18 hp blower with 4" ins and outs. The vac was about the same but the air volume was frighening. Gauge read 23" with valve closed and 19 with a fully open bleeder. Did the same test with the acrylic and it litterally sucked the acrylic out of my hand onto the bleeder board as it got close. I could litterally hear air being pulled though the 1/4" piece of MDF used as a bleeder. Just for grins and giggles, I put a 3" round puck on the board and even that was difficult to move. But, it also pulled a staggering 45+ amps - 3 phase 220 during the test. Also the price was out of my target budget range: $1800.

5) Becker 7.5 hp vein pump and also a variety of Alcatel pumps yeilded excellent results as well and was much more on the quiet side but they wanted an arm and a leg for them. I was quoted $2800 for the cheapest 7.5 hp (second hand) model and upwards of $5000 for one of similar performance to the 10HP 3" roots blower I ended up with.

That's long enough of an explanation for today as it's getting late so I'll leave you with a few pics.

One last thing: I got a great deal on a 10HP inverter through my Brother-in-law. $150 referbished "Rich" brand. I got this for soft start, RPM control, and power savings. More on this later. At this point the complete system is finished but I have not had time to take pictures. Here are the earlier pics of the blower itself:

vishnu Fri 26 March 2010 11:34

David,

That's a nice Vac pump and worth the price. Can you tell me the source of your purchase, i would love to have this setup. Waiting to see some videos of the pump working.

Gerald D Fri 26 March 2010 11:57

David, that is probably the best written research I have seen on vac holddown pumps!

(PS the correct spelling in this case is "vane" - seeing that you are a language school person :))

javeria Fri 26 March 2010 19:55

Ah very good writeup David, also put on a write up on the economics of running this along with mechmate -

liaoh75 Sat 27 March 2010 07:29

Vishnu, the place I purchased the pump was a very traditional machinery dealer. They don't do any business outside of Taiwan. They mostly support the local factories (of which there are many) in the Kaohsiung area which is near the southern tip of Taiwan. I'm sure you could probably source one in your neck of the woods. Taiwan is really strange as a tiny shop the size of a two car garage had this thing in stock. Their warehouse is located about 20 minutes away if I remember correctly. Not the most attractive place but they carried reasonably priced roots blowers and other types of pumps. Another shop located about 150 meters away sold the exact same pump for almost twice the price with no warranty. The primary market for roots blowers is fish farming where they have to aerate the water to keep their fish alive and these pumps run 24-7 for months on end.

Gerald thanks for the correction on the "vane" spelling. I wrote it at about 1:30 in the morning.

Irfan, the economics is quite simple. On the power consumption side of things, it draws about 30 amps from the inverter at full throttle. On the supply side of the inverter, it's only pulling about 21 amps. However, I find that there is no need to run at full power as 10-12" is more than enough to keep my parts from moving for my application. Under most operating circumstances, it's taking in about 15 amps from the inverter and about 7-8 amps from the breaker. How the inverter achieves this is a complete mystery to me but somehow, I can verify that the inverter makes a huge difference in terms of power consumption. Another big advantage is the fact that I am able to control the speed of the motor so I only use what I need.

Also, the vac hold down is a real time saver. Before, I had to make a tool path for screws which I found to be more effective at holding things down than the traditional clamp (No disrespect, Gerald;)). Also, the cut quality increased as there is less vibration as the bit cut through the material. Although I feel that vac hold down is one of best hold down methods around, I still have to agree with Gerald's earlier posts about vac not being the end all solution. It's just one more tool at your disposal when you need to get a job out quickly and don't want to play the 101 screws game. I read about massive pumps being necessary that were 20+ HP drawing a shameful amount of power. After my research, trial, and error, I can honestly say to the Mechmate community that you really don't need that much power on a 4x8 CNC router if you choose the right pump. My roots blower is still noisy (but acceptable IMHO) placed in another room and gets pretty hot, but for the price/performance ratio it's hard to beat.

I basically save about 15-20 minutes per sheet of material (compared to screws) using the vac hold down. Some people might think that's not a whole lot, but multiply that by 15 sheets and you should get the picture. How much is your time worth????? I have to squeeze every minute out of my day to balance two businesses, a very understanding wife (pregnant with our second child), and a two year old that want's daddy to play with him. Worth every penny if you ask me.

I will post more pics of the completed setup in the next week or two. I'm working on a new dust foot right now.

PEU Sat 27 March 2010 14:49

pardon my ignorance (for real no pun intended) how does a blower creates vacuum? a venturi?

bradm Sat 27 March 2010 16:34

Pablo, Roots Blowers generally have two equal sized ports. Depending on which port you use, you have either a big blower or a big vacuum. You then need to deal with designing the rest of the system. If you use it as a blower, you need a filtered source of lots of air. If you use it as a vacuum, you probably want a muffler system for the exhaust.

Alan_c Sat 27 March 2010 17:10

Thanks for all the info Dave, would you mind showing some pics of the vacuum table and manifold?

liaoh75 Sun 28 March 2010 00:16

Alan, I'm planning on doing just that. However, my shop is too messy right now. To be absolutely honest, I think messy is an understatement. I'm going to clean up a bit this week and take pictures after my dust foot is finished. I should be able to get pics posted by Sunday of next week.

liaoh75 Sun 28 March 2010 07:33

Good reading to on vac hold down for those interested:

http://geoteched.com/VACUUM%20INTRODUCTION.htm
http://www.techno-isel.com/cnc_route..._Hold_Down.htm

Prices like the one's mentioned on either of these links almost made me not even think about venturing into this method of hold down.

Travish Tue 30 March 2010 14:26

Does anyone have a source for these roots blower style vacuums here in the US?

bradm Tue 30 March 2010 14:42

Travis, I suggest you start with an E-Ebay search for "roots blower". That will give you a sense of the price ranges for new/rebuild/used/broken units. Then search for an industrial surplus / rebuilder in your area. These are large pieces of metal, and shipping will be significant. Note that if you don't have 30A of 3-Phase power to spare in your shop space, you probably don't want to be looking at these.

domino11 Tue 30 March 2010 15:40

Or the money to run them... :)


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