Lead in & Lead out

[Klaus Madsen]

I have tried to find some good explanations on the use of Lead in and Lead out, but can't really find any.

Anybody in here who can explain exactly what it is doing and when ad why you would use it?

Thanks
Klaus

[Dave Sheldrake]

So the high power strike when metal cutting doesn't cause spatter on the finished piece of work. On lower power machines it's used to avoid the very slight burn from the high power pulse at the start of the cut.

The laser fires outside of the works cut line and moves in gradually, it means the start and finish point of the cut don't show on the finished item

[Gary Hair]

Think of them like on-ramps and off-ramps on a freeway - you can't start out at full speed so you need a place to get going. Unless you're like 85% of the drivers here and this analogy won't make any sense whatsoever...

[Klaus Madsen]

Hi and thanks for your answers.

I fully understand what you are writing but it is difficult to understand why it won't make any marks if it starts firing slightly before it should and also after. I can understand what Gary is writing with the speed and acceleration that it have to start a little before to get up to speed but if it also firing at the same time??? Is it just me??? :)

[Dave Sheldrake]

Youtube "Mitsubishi metal cutting laser" and "ML2500 Mitsubishi" to see it in action :)

The first pulse of a metal cutting laser is at massive power to "Pierce" the initial hole in the metal, that causes a lot of spatter (molten metal flying around) to make sure this doesn't end up on the finished work the initial "pierce" is started away from the finished cut line.

In general on the sort of lasers discussed here it is rarely ever used.

[Kev Williams]

This is a lead-in/out routine as produced by Casmate (which it calls 'tangential entry/exit')
http://www.engraver1.com/erase2/tangential.jpg
First let me point out that the e/e points can be on the INSIDE of the letters or whatever you're cutting- it all depends on what you're keeping and what you're throwing out! ;)

Casmate was designed as vinyl cutting software, this routine helps-- because, whether you're cutting vinyl with a miniature swivel knife, or 1/4" steel with a laser beam or plasma torch, there is always one inherent problem:

The start point and end point is the same point.

With vinyl, what can happen is the start/end point ends up not being cut at all, because the point's don't overlap. This makes weeding a nightmare because the uncut point is like a tab you have to break...
--the lead in/out creates the overlap, and weeding is a breeze because there's no connections anywhere along the cut path...

Now, throw a bunch of heat at the start/end point from a torch or laser beam. To start the cut, the heat source isn't even moving, and must be "on" long enough to get at least halfway thru the material before accelerating to speed. And when the heat source returns home to the start/end point, it must decelerate and then stop.

...Not only is the start/stop point the only place the heat source appears twice, in both instances it's either stopped or moving at it's slowest pace.

BUT, by using a tangential entry and exit, the heat source still passes the same point twice, but at full speed. The start and end points are now different, and away from the actual work. This allows the laser or flame to be in full swing by the time it reaches the intersecting points the first time, and it will cross the intersection on the return at full speed, with plenty of time to slow and stop at the new end point. This will render the least amount of overburn possible at the intersection !

[Klaus Madsen]

Wow Kew, thanks for a great explanation. Very understandable!
There should be a place in the Forum where we can keep kind of useful stuff.

So the setting for the lead in and Out is that trial and error to find the best setting?

Thanks again
Klaus

[Bill George]

When I had my PlasmaCam and cutting metal it was needed, I have never seen a need with my laser engraving machine.

[Jerome Stanek]

I use a lead in on one of my ongoing jobs it helps as the start point is a very sharp corner

[Kev Williams]

So the setting for the lead in and Out is that trial and error to find the best setting?

As for Casmate, you can choose the radius of the in/out arc. In my sample, the arc I used is much larger than needed for vinyl cutting, probably about right for laser cutting, but might need to be bigger for plasma cutting- I've watched a few videos of those things in action, and it seems the farther from the intersection you can get, the better! As for Casmate, it locates the origin itself. I'm sure there's other programs that do this, but I don't know what they are? Anyone with editing skills can make their own in/out points. No law that the entry-exit has to be curved either, just straight lines away should suffice in most cases...

I use it mostly for vinyl cutting. There is one job I do for a customer, it's 2" diameter round acrylic piece with 3/16" holes and a small rectangle for an LED readout-- I use the lead-in/out when making those parts. You literally can't tell where the laser starts/stops the cut... :) --and it starts the rectangle cut right in the middle of the longest section, so all four corners get hit exactly the same.

[Keith Winter]

Awesome explanation Kev!


This is a lead-in/out routine as produced by Casmate (which it calls 'tangential entry/exit')
http://www.engraver1.com/erase2/tangential.jpg
First let me point out that the e/e points can be on the INSIDE of the letters or whatever you're cutting- it all depends on what you're keeping and what you're throwing out! ;)

Casmate was designed as vinyl cutting software, this routine helps-- because, whether you're cutting vinyl with a miniature swivel knife, or 1/4" steel with a laser beam or plasma torch, there is always one inherent problem:

The start point and end point is the same point.

With vinyl, what can happen is the start/end point ends up not being cut at all, because the point's don't overlap. This makes weeding a nightmare because the uncut point is like a tab you have to break...
--the lead in/out creates the overlap, and weeding is a breeze because there's no connections anywhere along the cut path...

Now, throw a bunch of heat at the start/end point from a torch or laser beam. To start the cut, the heat source isn't even moving, and must be "on" long enough to get at least halfway thru the material before accelerating to speed. And when the heat source returns home to the start/end point, it must decelerate and then stop.

...Not only is the start/stop point the only place the heat source appears twice, in both instances it's either stopped or moving at it's slowest pace.

BUT, by using a tangential entry and exit, the heat source still passes the same point twice, but at full speed. The start and end points are now different, and away from the actual work. This allows the laser or flame to be in full swing by the time it reaches the intersecting points the first time, and it will cross the intersection on the return at full speed, with plenty of time to slow and stop at the new end point. This will render the least amount of overburn possible at the intersection !