Messages

1111

General Mach Discussion / Re: Shielding Issue and Mach3

« on: July 01, 2009, 11:27:28 AM »

Looks like I'll have to bite the bullet on this one and rewire. That's going to take some time. Hopefully shielding the wire will take care of this.

At any rate I was able to get some things accomplish... heres one: http://www.brightstarlinks.com/006%20cropped.jpg

Hey!  Are you giving us the bird??  :-)

1112

General Mach Discussion / Re: Shielding Issue and Mach3

« on: June 30, 2009, 09:34:31 PM »

Thank you for replying Greg.

Sadly, changing the debounce had no affect what so ever. As soon as power is applied to the breakout board, controllers and steppers the message "limit switch triggered" begins flashing and an emergency state is present. I reset and within 2-3 seconds another message "limit switch triggered" happens. I carefully installed all the wiring and rechecked to make sure there are no shorts. Again, in diagnostics, the green LED's are lit indicating a signal from the parallel port is present and no yellow LED's are lit for the limit switches.

Any other thoughts?

Also, HimyKabibble ... I appreciate the input... I wired the limits normally closed since it was part of the instructional video as the "safest method" to use, Also, it allows me to run home and away limits in series since I am limited in the number of inputs on my parallel port. The break out board only has one hook up for one parallel cable. As far as running separate wiring for the 5v's that's no problem.

Now to the shielded cable, what size would you recommend for the signal wire? 22, 20, 18 gauge? Solid core or stranded?

And, excuse my ignorance of acronyms, but what is a "BOB".

Thanks for the help,

Don

BOB = Break-Out Board.  Wire gauge/solid/stranded is irrelevent - except any wires subjected to flexing as the machine moves MUST be stranded, the finer the better.   These a low current/low voltage signals, so any wire will work.  NC limits are OK, but I would still put a stiff pullup resistor (like less than 300 ohms) on the BOB input, and let the switches pull the signal to ground.

Regards,
Ray L.

1113

General Mach Discussion / Re: Shielding Issue and Mach3

« on: June 30, 2009, 08:26:07 PM »

First, you have things wired backwards from the way I would do it.  E-Stop should *always* be wired NC.  Otherwise, if the switch fails, you won't know until you need it, and it doesn't work.  The Limit/Home switches should be wired NO, so they pull the BOB input to ground when the limit is reahced.  They should also have stiff pullup resistors on them, so it takes a reasonable current to pull the lines low.  *All* the signal wiring should be shielded, with the shield grounded *only* at the BOB end.  *All* grounds in the system should connect to a single point, preferably on some hefty metal piece, like an enclosure.  Never, ever daisy-chain ground or power connections.  Use the de-bounce in Mach if you have to, but I'd first get the signal quality cleaned up as much as possible, and use the debounce as a last resort.

Regards,
Ray L.

1114

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 29, 2009, 12:26:50 AM »

NOW for the rest of the story (;-)  how are you going to index the spindle to the correct position each time. NO easy feat on a BP type machine. The mechanism is quiet simple but fitting it in a manner that works well is not.

Was not a problem with teh tormach style of holders BUT(;-) any style with a keyed holder it is vital.

Just another though, (;-) TP

Terry,

The short answer is:  You don't.  You MUST remove the pin from the spindle.  I can't for the life of me understand why that pin is there anyway.  It serves no useful purpose.  If the tool is too loose, it'll just shear the pin off.

Regards,
Ray L.

1115

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 10:03:35 PM »

Ray I have used R8 for a LONG time and I NEVER depended on the R8 collet to hold anything(;-) tool creep was always a problem UNLESS you pulled the drawbar like a madman. NOW an R8 toolholder with a collet set was OK as the nut contained the tool quite well.


With a R8 toolholder just a snug up and it was fine. Never really figure out why the R8 collet came about other than just cheap.

Just a thought, (;-) TP

Terry,

Interesting - For endmills, I've never used anything but collets, and never had one move on me....

Regards,
Ray L.

1116

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 08:34:24 PM »

The Matchmaker was an Int 40 taper so no alignment screw in that.
  I had an Aussie Power Drawbar on my manual Bridgeport years ago, crossthreading  never happened in all the years I used it.
Hood

Hood,

Oh, I thought you were saying it was R8.  Now it makes more sense.

Regards,
Ray L.

1117

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 06:57:11 PM »

What I haven't heard is why the impact wrench is so poorly suited to an ATC, because it does solve all these problems and is a proven design.

Best,

BW

And also works very well, the toolchanger I have aquired for the Beaver mill was originally fitted to a Matchmaker and that uses the impact wrench type power drawbar. When I went to see the toolchanger I was amazed at how well the impact wrench worked, just wish I had taken a vid of it working before the changer was removed.
Hood

Hood,

So I assume the alignment pin in the spindle has to be removed?  I've always been curious what prevents the drawbar from getting cross-threaded?

Regards,
Ray L.

1118

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 06:53:06 PM »

Below is a solution to the release force problem - a very compact and simple mechanical force multiplier.  The green housing is stationary (attached to the power drawbar structure)  The conical piece is connected directly to the piston of the air cylinder, with the air cylinder pushing straight downward.  The cup-shaped part is the plunger that presses on the top of the drawbar to release the tool.  The red shows the position when the tool is engaged, the blue when the tool is released.  Basically, the air cylinder pushes the conical piece down.  This causes the ball bearings to roll along the surface of the conical piece, and at the same time outward along the ramps on the housing.  This motion forces the plunger downward.  As drawn, this provides a 10:1 mechanical advantage, which means my existing 490# air cylinder would generate almost 5000# of downforce, with 0.150" of travel.  The rest of the assembly remains exactly as it is now, with the (now very short - only 2") - guide tube added to the top of the spindle, the same mechanism to prevent that 5000# force from being applied to the spindle bearings, and the same mechanism to "pop" the collet free from the taper.

Regards,
Ray L.

1119

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 04:33:48 PM »

The Mach1 system reveals the secret here.  There are really two issues to consider.

First is locking the tool holder to the mill.  That's going to be a function of the surface area of the R8 taper and the pull force.  I am not too surprised that 600 lbs suffices for that force, even with quite a lot of "work" being done by the spindle. 

But there is a second force, and the way it works is hugely counterproductive to the first.  That second force is the squeeze on a collet to hold the tool.  It doesn't exist with solid tool holders, and it is the reason the Mach1 system has that special R8 collet holder.  It's purpose is not only to squeeze the collect down on the tool and not only to provide a reference datum so Z is repeatable.  It's alternate purpose is to provide a clean r8 taper surface on the tool.  You can see this clearly on the patent illustration:

http://www.google.com/patents?id=8mgWAAAAEBAJ&printsec=abstract&zoom=4

Why is this so important?  Because the deformation of the collet as it locks down on the tool really interferes with its ability to make good contact with the R8 taper.  If you think of bluing tapers, there is no way in heck that there is much precision in that interface.  So now the drawbar force must not only provide sufficient clamping, but it must also combat the reduced surface area and hence friction of the collet in the taper.  The Mach1 system avoids all of that.

Folks get started on these air-cylinder only systems because they seem simpler than an impact wrench system.  But they're really not unless you're prepared to live with a huge amount of drawbar tension, and even then I wonder how well they are going to work with a facemill or a large silver and deming bit.  People keep saying that this has been tried over and over, and it has.  The drawbar manufacturers would love a simpler cheaper mechanism, if only one would work.  Yet they keep shipping impact wrench based systems for R8, or special patented tricks like Mach1.

What I will tell you is that a rookie machinist can build an impact wrench system in an afternoon and it won't suffer from any of these problems.  It can be completely automated for use in an ATC if desired.  It's simpler and cheaper.  Your biggest challenge for the ATC is that you'll be using solid R8 holders which don't have a standard interface for the ATC carousel.  That's no big deal.  You'll need to fab some collars for the tooling that serves that purpose.  Meanwhile, you will be saving a fortune on TTS holders and you'll have a more rigid system to boot.

Cheers,

BW

Bob,

You seem to "know" things that nobody else seems to know.  For example, the required drawbar tension.  I looked high and low, and could find *nobody* that could give me anything more concrete than numbers they pulled out of the air.  I even asked Tormach - had several e-mail exchanges with several of their engineers, in fact - and THEY have no idea!  They asked me to send them any information I come up with!  So, I went with what I had, and best guesses, which turned out to be too low.  I looked at what Hoss and others did (only 500#, BTW), and assumed I'd need at least twice that, due to the far more aggressive cuts I can take.  Even that estimate was too low, by a factor of 2-4.  So, had I had a good number at the outset, I never would've gone down this road.

Saving a fortune on Tormach holders?  I always planned to make my own, so cost was almost $0.  No savings at all there.  The commercial drawbars out there are just that - drawbars.  I don't think any of them, even the Mach1, are intended for use in an ATC, so it's apples and oranges.  Were I after nothing more than a power drawbar, I would've built the impact wrench kind a LONG time ago.  It's cheap, simple, and works.  But it's *not* well suited to an ATC, which was always my goal.

As for "this has been tried over and over" - I've spent most of my career doing things most others told me could not be done.  And, more often than not, I've succeeded.  So, for me, the fact that nobody else succeeded is hardly reason to scrap the whole idea, unless I know *why* the others failed.  In this case, I did not, so I decided to give it a try and learn for myself.  If nothing else, I've learned a few things that I'm sure will come in handy down the road somewhere.  And I still believe this approach *can* be made to work, and the cost would not be THAT much more than the impact wrench kind.  I can now see good solutions to *all* of the problems., even the high drawbar force requirement.  It's now down to whether the additional time, money, and effort to do it is worthwhile, given that I have no shortage of other projects I need to get to.  I may well go ahead with something else for now, and complete this in the background.  It absolutely CAN be done - I have no doubt of that at this point.

Regards,
Ray L.

1120

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 02:27:51 PM »

RAY here is the Youtube example

http://www.youtube.com/watch?v=6CChUHOAknc

With you upper mech and this lower setup I believe you will be just fine (;-)

Just a thought , (;-) TP

Terry,

First, I haven't given up yet, but I'm close.  And not because anyone else said it wouldn't work, but because I have other things to do, and this project has already taken far more time and money than I had hoped.  I originally considered both this approach, and the impact wrench approach.  The impact wrench had the advantage of being dirt cheap ($50?), though it seems crude to me.  This approach had the (apparent) advantages of simplicity and elegance.  However, the decision was based on the assumption that the required drawbar tension was in the 1000# range.  This assumption was wrong - the required tension is as much as 5X that, which gets very difficult to deal with.  Had I known that at the outset, I would never have gone down this road.  Getting above about 2000# becomes quite difficult.  What I have, even in it's original incarnation, would work just fine on a small mill, like and X2 or X3, with perhaps 1000# tension, but is not up to the loads of a full-size knee mill.  I am running production, so going to smaller tools/more passes is REALLY unattractive.

That one in the YouTube video is an X3, and I'd be willing to bet the owner considers a 0.100" cut with a 3/8" endmill to be *really* heavy.  I run all day long at 1/2" DOC, or more, at fairly high speed (30+IPM), so having a tool pull out would be a very bad thing, in terms of scrapped material, lost time, and potential danger. 

In retrospect, I tend to think the impact wrench approach is the simpler, cheaper, and safer, way to go.  But I still think it's crude.  Adding a pull-stud does nothing to mitigate the problems with this approach, unless I give up collets entirely.  It is the very high drawbar tension requirement that is the issue, and that is just a fact of life with R8.  I am going to consider this approach - in fact, I did very early on - but it presents a different set of problems.  For one, I don't know how you make an ATC to swap R8 tools.  At a minimum, it would require removing the alignment pin, which I'm not real keen on.  It greatly increases the vertical room needed to make a toolchange - though at least alignment would be easy, since the "mouth" of the spindle is so large compared to the top end of an R8 tool.

Regards,
Ray L.