Newbie- Positioning Material Accurately

[Brenck]

Hi guys,

I have a homemade cnc mill 3axis and I mostly machine aluminium, always from rectangle bars, like 2''x 5/8'' and bigger, I buy it from bars instead of sheets because its cheaper here. Most of the times I face the sides of the material to the desired length and then I mill the holes that I have to on the part, lets say its a 2''x5/8'' bar with lenght of 300mm, I chop the bar with lets say 310mm and the face the sides with a endmill, after that i run the g-code that cuts holes and pockets on theese parts...

But the problem is to set the tool on the material, I don't have a toll setter or anything like that, no money at the moment to buy one either. Axis Z its not a big deal, its ok to set it, but X and Y I never do it right. Lets say this parts have 5 holes on it, all equally spaced, the middle hole needs to be centered on the material on both directions... No matter what I try to do it finish a little off like 0,5mm or more...

Sorry if its a really newbie question

Thanks everyone

[ironDigit]

if you squared off both sides down from 310mm to 300mm and do the drilling in one set-up you'ld exactly know were your workpiece is without any additional tools.and be able to workout the center with this info or atleast any cncprog should.

if this doesn't solve it ,did you look into the backlash on your machine already?or maybe bad centering etc. etc.

good lukk

[Shotout]

Get a good quality edge finder. IF your vise, assuming your using one, has been indicated in then you can edge find off the stationary jaw of the vise then offset that by the radius of the edge finder tip to set a known Y position. I generally use it for Y 0.0 if I'm not machining along that face of the material. Once you sidemill one side of the material square you can offset that by the diameter of the endmill and set X 0.0. You can use that and the diameter to accurately find X300mm for squaring the other side. Then your machining should be properly located in the material.

Originally Posted by Brenck Hi guys, I have a homemade cnc mill 3axis and I mostly machine aluminium, always from rectangle bars, like 2''x 5/8'' and bigger, I buy it from bars instead of sheets because its cheaper here. Most of the times I face the sides of the material to the desired length and then I mill the holes that I have to on the part, lets say its a 2''x5/8'' bar with lenght of 300mm, I chop the bar with lets say 310mm and the face the sides with a endmill, after that i run the g-code that cuts holes and pockets on theese parts... But the problem is to set the tool on the material, I don't have a toll setter or anything like that, no money at the moment to buy one either. Axis Z its not a big deal, its ok to set it, but X and Y I never do it right. Lets say this parts have 5 holes on it, all equally spaced, the middle hole needs to be centered on the material on both directions... No matter what I try to do it finish a little off like 0,5mm or more... Sorry if its a really newbie question Thanks everyone

[Boots]

I take it this is a Flat Bed Router and you do not use a vise to hold your part. If so you need to do what I do. I machine a fence to locate the part and position a stop on one end. This way I know exactly where the edge is and can program the part from there.

[mc_n_g]

Do what Boots said. I would make a 'L' shaped fence to index the part when you put it in. This way the corner of the 'L' is your key position. On the other side I would use toe clamps. Check out mitebite.com for some ideas for clamp styles.

[Brenck]

I was writing a huge repply and somehow i got an error that wasnt able to crtl-c ctrl-v after it, chrome didnt backup either... = (

But basically, I used the 300mm part as an example, not always that size, I use a vice kind of thing but the jaws are wider then 300mm, so I just have one free end to square at a time.

I can machine using clamps on the table but depending on the part i cant because i take it out from the alum. bar

If I cut the same part a lot I would do a custom fixture or something but most of the times I dont cut more then 2 of the same...

The mitebite website you post doesnt seems to work...

I might use a edgefinder, is there any homemade device that can be used as a edgefinder?

Thanks for all replies

[sti2011]

A dowel pin of known dia. or any other round item, can be colored with magic marker and when it contacts the material (at a very, very slow feed rate) when rotating, the ink will smear, then move up in Z and move over 1/2 the dia of the dowel pin. Really low buck but it will get you pretty close.

[Brenck]

Oh thats nice, I will use a broken drill, this kind of precision will be enough for me.

Thank You

[mc_n_g]

Sorry I mistyped it. miwww.miteebite.com
Look up edgefinder on YouTube. There is a nice Tormach video showing use.