4.1 inch hole is 3.97 on wood. Why? Can you help me get 50 IPM?

[Revtech]

Hello I have built the large router from David Steele. It works great for the most part. But I have a problem that I'm looking to fix. I want a 1 inch hole to be 1 inch. Or in this case I want a 4.1 inch hole to be 4.1 inches. I use Mach 3 to run my G code. and a buddies Artcam insignia seat in the eve to create the image. My motors are Xylotex 269 in motor kit. I feel like the answer is in mach 3 But I'm not sure. If I'm not wrong I think when I was playing with mach 3 there was a time I changed the size of something by changing the steps or something.
Also Can someone explain about using more voltage to get faster IPM speeds. I can run at 35 IPM but nothing else better be happening and the planets need to line up to create perfect line or the motors stall. I have realized that if I turn down the IPM to 22 I can even surf the INTERNET or even work on the next project. I want this to be level of stability at 50 IPM or higher can some one help me figure out what to do to get there? Well thanks for the info in advance! Rev.

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[ger21]

You can adjust your steps per unit (motor tuning screen) to better match your leadscrews, but you should do some testing to make sure it's accurate at different sizes, and different locations on your machine.

Since the Solsylva website specifiess that you'll only be able to cut at 30ipm, you may need to make some major changes to go faster. Not sure, but I think I read somewhere that they use 5/16-18 threaded rod for leadscrews? If so, the cheapest way would be to switch to 1/2-10acme, or maybe even 1/2-8 2 start acme screws and nuts. This will probably require a lot of redesigning of the screw mounts. I've never seen the plans, so hard to say.

I don't know what voltage you're running at, but the Xylotex is limited to 30V, so increasing the voltage probably isn't really an option. (Unless your'e running at 12V). I don't thinik you want to spend $500 on new drives, power supply and motors to go that little bit faster. You could try a HobbyCNC drive, but you'll need different motors and power supply, and I'm not sure you'd get a solid 50ipm with that upgrade.

I'd say change the screws. Guys building Joes design are using 1/2-10 acme and getting 100+ipm out of them with a Hobby CNC, maybe a little less with a Xylotex.

[edo]

Are you using tool offsets in your G-Code? If not, you need to account for the size of the cutting tool in your drawing. A 1/8" bit cutting right on the the vector will cut 1/16" of material away on either side of the line, giving you holes that are 1/8" smaller than the drawing.

[SORCHEROR]

revtech , we need more info.first,lead screws or ball screws?threads per inch
or pitch?direct drive motors?if pulleyed,what ratio?also what are the micro steps set to on the driver,full,half,1/4,1/8,what power supply voltage?to run higher speeds and keep from stalling the more volts the better,your drives max at 30v,i would run them at 30 volt supply,hard to find though,im not sure on the xylotex drives,but most of them you must set(with a trim pot)for the amp of the motor,using a volt meter,anyway give some more info please,and id be glad to help.
steve

[SORCHEROR]

another note,people like to set there drivers to the 1/8 micro steps for the smoothest operation,but you loose power and top end speed,with also can loose accuracy,half step is a good start point if you want more power and speed

[Revtech]

Excellent feedback! I will get the info tonight. Thanks again for the fast replies! Rev.

[Zumba]

Are your holes perfectly round? A perfectly round hole *may* rule out mechanical problems. A hole with flat spots indicates hysteresis caused by flexing of critcial components such as screws, bearings, and even structural elements.

[Zumba]

BTW, here's a test you can do. Cut a 4.1" hole and also cut out a 4.1" circle (different offsets of course). If the circle fits perfectly in the hole, then it's probably a software issue.