Stiffer frame

When you grab the tip of the bit, what moves? You are approaching this very strongly from a theoretical point of view, which does not factor in all of the various components (like when a professor says, just neglect the forces of air resistance). Yes every little bit helps but there are much lower hanging fruit that trying to make steel more rigid. If you want it more rigid get get thicker wall, 100% less time and money is wasted that way.

You have a machine, wiggle it from where the force will be applied, what happens?

Aside from reprinting the parts, what would you suggest to make it more accurate. I’ve decided a cut area of 2’ by 2’ by 2" is great for my needs. I will be using mid span supports. I will be cutting anywheres from 6000rpm up to 18000. I have an assortment of O-flute cutters ranging from 1/8 to 5/16. My main concern is accurate over speed. Mainly I will be milling hdpe.

Make is shorter. 2 foot tall is waaaaay too tall. 4 inches max! You’re also not going to need mid span supports for a 2 foot tube.

 

This was milled on my 5 foot square machine, it was only 4 inches tall, and still is, though now it’s about the size you’re planning, just shorter.

Accuracy is easy, you should be using a finishing pass at all times. Done, stock machine fits this requirement very easily 100%.

If you haven’t used it yet, try it first. There is absolutely no reason to think about modifications without use first. There is nothing that can not be easily and cheaply changed later.

 

I have a lot of it assembled. I had to reprint a couple of parts. Should be this weekend for it’s first move.

I feel like what you are doing is pointless.

Unless you really have some crappy marshmallowish tubes, there is close to no point in stiffening that part for wood or HDPE milling. If you feel like it is really an issue (which again, I doubt it will), then just purchase some bars made of chromoly and you should be good for any kind of load you want. Especially since the machine you plan to build is actually not that big (you mentionned 4 feet).

What might need to be stiffened on the MPCNC is the Z axis, the other ones are just fine.

My advice is: don’t overcomplicate things when you don’t actually need to. First build the machine following the actual original specs, familiarize yourself with it and then, only then, make the necessary improvements, if any.

 

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Ok did as you said. The machine is assembled. There is a good amount of flex in the gantry when force is applied. Is this what you are referring to when you say it’s not going to matter making the pipe stronger? It’s already stronger that the gantry?

Whoa…easy, careful with the wording. You were quoting numbers and figures earlier, stick with it.

If you apply force at the endmill, what moves? How much force (about) do you need to apply to move it. You did math and stats earlier in the post, don’t get sloppy now. The endmill tip, the last .5-2mm is the only part that will resist the forces applied. You can imagine the forces it experiences on a single flute with a .001 (recommended) load per tooth is minuscule, so no telling me 10lbs of force to flex the gantry. The best way to measure this is X amount of force deflects the endmill X distance, at X amount of distance from the bottom of the gantry.

This is exactly what we are trying to get at, the load of a properly set up cut is next to nothing. Too much load and you are exponentially increasing the forces, to little and you can work harden or melt. A proper cut is a very mild force.

Most people mistakenly grab the X axis and flex it with 10-20 lbs of force (Tom’s interview with me), that means nothing.

You can use a scale and a dial indicator to easily get these numbers.

Another fun thing to try is test it at zero stick out of the gantry and at full z depth and look at the percentage difference. Half stick out should be more than twice as rigid.

I love real numbers, you can tell the theoretical stuff doesn’t sit well with any of us.

In the world of armchair engineers, standup.

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Ok. I think if we added a bit of plastic where my finger is sideways, and added a 6/32 in the two places I’m pointing vertically it will make the gantry a bit more stiff. Not sure how much but I could mock it up with a block of wood for the gap and simply drill the holes, and use some washers.

 

You have to try it first.

Use the machine.

You have many many hours worth of CAM to learn before you worry about changes to any hardware. So many other things that would be a much better use of your time than guessing about the structure. You have CAD, CAM, bit selection, material hold down, prices, time involved, material costs, dust, noise, tolerances, proper part design, etc.

Please, please try it before you bother with any of this.

How many ounces of force caused that part to move?

I’ve run a mill and lathe before and have used solidcam and aspire. I have some computer programming under my belt and helped port linuxcnc from Debian to Linux mint and Ubuntu.

If it wasn’t for the fact I have a few days off printing left on three printers i would finish this.

I need a case for the controller, reprint a bottom corner, dual endstop parts, and z max. I’m waiting for the LCD.

You can ignore my posts if you like.

However I mocked this up with nylocks inside and it helps. It wouldn’t take much to add some screw ways and a spacer.

I should have added one more facing down but forgot. Still helps a bit though.

There is a 5", 5/16" bolt right there, and 4 flanking that. That really should see no movement, if built correctly. For my builds that is not the source of flex. Matter of fact I can not make that part move in any way even picking the machine up by the gantry. I have one directly next to my desk.

If that really does move for you try a drop of CA glue top and bottom, or try a rebuild of the gantry it should not move.

Again, how much force for the tip of an endmill does it require for that to move. I have a deep down gut feeling you are really seriously over estimating the cutting forces the machine experiences. You seem to be looking for a smoking gun, it is just a balanced build. Better rails won’t help without more rigid parts, more rigid parts are larger, larger parts require more power to move, more power is more expensive. A few upgrades and you have upgraded right to a tormach, the small ones are cheap.

I urge you to enjoy having the ability to have a CNC machine at your house that can cut aluminum without taking out a loan and running 220V or 3 phase power. Everyone who has commented in this thread here has pushed the boundaries and made me second guess the machines capabilities on a weekly basis and I love it. Front page, Omri has used it with a fashion designer! Barry 5’x5’ build, Dui 18" Z and all sorts of other stuff. Proving something works, with actual proof is amazing, I love it and hope to incorporate improvements along the way that make sense to the project as a whole point just a niche use. That is the whole point of being as open as I am with my designs. I encourage people to call there changes “mods” and make them available so others can decide to use them or not. If I think it is a poor choice for some reason I will contact you privately to voice my opinion so you can chose to make changes or not. If I love it I will ask to include your change and usually name it after you or whatever you prefer, the “heffe plate” is one such change. Making a thread full of guesses of all my design choices honestly casts doubt on the design as a whole for the less experienced and will most likely will push them to try something else that may or may not be better.

  • Casting doubt on your designs, is not my intention.
  • I am looking for such mods, and it's not like they are all in the same place. I have seen many on thingiverse, but it is imposible to know which have actually pushed the boundaries and which are just designs.
  • Again I originally wanted to have a cutting area of 2' by 3', but it seemed as you had a protest to this, citing the availability of the lowrider.
  • I'd love to have a larger z axis of about 5 1/2 inches.
  • Right now I'm hearing a lot of what not to do, which is fine. It's helpful.

The absolute best thing to do is try it as I have laid it out. This is the best collection of parts in my oppionion, I stakw my income on this fact. I address how I handle mods in the previous reply.

If you want to change something you have to have a baseline to compare it to anyway. Have a little trust in my oppionion. When the time comes for your mods I will return the favor.

Where are the mods at again? I must have missed that part. Sorry.

Thingiverse, search mpcnc

We’re just back at guessing as to which will really improve the machine. I see a belt tensioning mod, but as I understand it, tightening the belts too much is a bad thing.

Maybe you could add the mods you approve of in a collection label mpcnc mods on your thingiverse. That way there is no confusion as to which mods you support. :slight_smile:

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Also, where we’re we’ looking to find stainless tubing so cheap? What was the wall size again?