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Thread: CNCRP Benchtop Pro or Standard 2424

  1. #25
    Member mithiral67's Avatar
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Quote Originally Posted by ger21 View Post
    If you are using a 1/4" tool or larger, cutting noise will usually be louder than the spindle. The exception would be with very light passes, at very high rpm, where the spindle is at it's loudest.

    For example, my machine is in my attached garage, and my family room on the other side of the wall. When in the house watching TV with the machine running, I only hear it when it's actually cutting.
    Hmm, we have pretty good sound proofing between units, but will definitely ask the neighbors if they hear anything to ensure I am being a good neighbor.

    Ok, down to the last decisions.

    Do I go with the Benchtop Pro 2424 for the Pro4824. They both weigh in around 250lbs, and based on my mill research, the more weight in a given package size the better it is a milling metals. Being close to 1/2 the size, I would have to assume the Benchtop has to be a decent amount more rigid. Does the ball screw vs rack and pink drive impact that? The ballscrew is the preferred method of heavy milling, so I assume the best. Does rack and pinion create a loss of rigidity under force?

    All that being considered, does it matter? Will both do a similar job? Is the sacrifice of stiffness worth the extra 2 feet or vice versa?

    Doing a little research, its clear the CNC's offered in the range I am looking at, note that they are good for aluminium and softer. They don't even come near to recommending for steel or harder. When looking up the hardness of aluminium to steel, its usually only a .5 to 1x increase when looking at various types. Its crazy that not even a double of harness can go from fully capable to not even recommending it. So much for me to learn.



  2. #26
    Community Moderator ger21's Avatar
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    They don't even come near to recommending for steel or harder. When looking up the hardness of aluminium to steel, its usually only a .5 to 1x increase when looking at various types. Its crazy that not even a double of harness can go from fully capable to not even recommending it. So much for me to learn.
    The simple answer is that it's not that simple.

    I just did some searching, and found a chart that stated the Mohs hardness of steel can be 5x more than aluminum.

    But I think that steels other properties are more important than hardness. With aluminum, the harder alloys can actually be easier to cut, because they are not as gummy.


    Being close to 1/2 the size, I would have to assume the Benchtop has to be a decent amount more rigid. Does the ball screw vs rack and pink drive impact that? The ballscrew is the preferred method of heavy milling, so I assume the best. Does rack and pinion create a loss of rigidity under force?
    I'd call or email CNCRP and ask them which machine they feel is more rigid. Tell them what you want to do with it, and ask their recommendation?
    I would expect the 2448 to use larger, more rigid components. But yes, the larger size allows for more flex.

    I don't think that you'd come anywhere near exceeding the force holding the pinon into the rack, so it houldn't be noticeably less rigid.

    Gerry

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  3. #27
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Hi Mithiral - It's not the hardness that makes cutting steel "harder" its its stiffness and strength. Steel is three times stiffer then aluminium and most steels are much stronger then aluminium. So the cutter has to overcome the metal stiffness to start a cut (so you need 3x more effort to deflect the chip) then the tool has to shear the metal, steel being stronger needs more power and these are multiplying factors not additive. Then if the machine is not stiff enough to keep the tool steady it will never start a chip it will just deflect around the cut then slide along the surface resulting in blunt tools etc. Really need a mill for cutting steel. Look up chip load charts and power charts for cutting and you will get an understanding. Mills look like mills and routers look like routers for a reason. Peter

    To put this in perspective and only consider the materials stiffness as a basis. The tool has to deflect the material to start a chip then the tool has to shear the material to remove the chip. The stiffness of plastic is 3000 to 4000MPa. Sorry I'm metric (1MPa = 0.15 ksi you can do the math) The stiffness of hardwood is about 20000Mpa the stiffness of aluminium is 70000Mpa and steel is 200000MPa. For interest titanium is 110000Mpa. So a machine designed to cut plastic and timber at best needs to be 200/20 = 10x stiffer to cut steel. This is a huge difference and this is a simple comparision approach. When you take the material strength and other factors into scope its a very serious upscale to get to a mill machine. You can cut aluminium in a router but its a compromise on feeds and depth of cuts and tool wear to get it happening. Otherwise mills would look like routers as they are cheaper to make. Cheers 2 Peter



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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Quote Originally Posted by wmgeorge View Post

    My air cooled spindle does not blow dust around. You will need a dust collection system anyway. Water cooled is a pain. I had one and my laser is water cooled also. Unless you run a sealed system with a refrigerated chiller like my laser, you will need to deal with algae.

    I use a water cooled 2.2kw spindle and am happy with it. I don't find it to be a pain at all.

    You can avoid the algae problem by using RV antifreeze (propylene glycol), What I use has corrosion inhibitors and is pet safe (although my two dogs don't ever get anywhere near it), I have a couple of gallons in my holding tank (aka poly storage bin) where it has been for the last couple of years. Nothing growing in it. You can pick it up at Wally World for about $2.50/gal. If you get a concentrate (I don't), be sure to use distilled water to dilute it. Don't want a bunch of minerals trying to clog the spindle coolant passages.

    I use a 12V submersible pump (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1) and and a small, 2 fan, computer radiator. Router stays nice and cool - never gets even slightly warm. It's surprising how little liquid flows through it. Little more than a trickle. Does the job though.

    The air vs water cooling is a long running debate. It's just a matter of what you land on. When I bought mine, most folks seemed to lean toward water cooled, so I went that way. If I had to replace my spindle, I'd probably stay with water cooled. But that's just me. Your mileage may differ.

    I can attest that water cooled are pretty quiet when not cutting, but the noise level goes up significantly when it's cutting. I have never owned an air cooled spindle, so I can't offer any comparisons on noise.

    Gary




  5. #29
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Quote Originally Posted by ger21 View Post
    The simple answer is that it's not that simple.

    I'd call or email CNCRP and ask them which machine they feel is more rigid. Tell them what you want to do with it, and ask their recommendation?
    I would expect the 2448 to use larger, more rigid components. But yes, the larger size allows for more flex.
    Yea, I didnt get far into the research, obviously a lot to learn.

    I did call and ask about the pro vs standard on stiffness and they werent very helpful, ha. It was pretty vague, yea, pro is stiffer. Would be great if there was more than just resolution, accuracy, and repeatalbity. Like 1,000 of a inch deflection when 25lbs of force are applied to the spindle bottom. Probably thought of, argued over, and never adopted.

    Quote Originally Posted by peteeng View Post
    Hi Mithiral - It's not the hardness that makes cutting steel "harder" its its stiffness and strength. Steel is three times stiffer then aluminium and most steels are much stronger then aluminium. So the cutter has to overcome the metal stiffness to start a cut (so you need 3x more effort to deflect the chip) then the tool has to shear the metal, steel being stronger needs more power and these are multiplying factors not additive. Then if the machine is not stiff enough to keep the tool steady it will never start a chip it will just deflect around the cut then slide along the surface resulting in blunt tools etc. Really need a mill for cutting steel. Look up chip load charts and power charts for cutting and you will get an understanding. Mills look like mills and routers look like routers for a reason. Peter
    Thanks Peter, yea, sounds like a lot more going on than the couple of charts I looked at

    Quote Originally Posted by GME View Post
    I use a water cooled 2.2kw spindle and am happy with it. I don't find it to be a pain at all.

    Gary
    I will need to go and do some more reading to make sure I make the best choice. Thanks for your thoughts.



  6. #30
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    RV Anti freeze is not 100% algae proof, I have had it in mine. I think its DowTherm is the chemical we used in solar systems? I am hoping my system does not have algae again it was a pain to get cleaned up. YMMV. I may go to standard automotive anti freeze made for aluminum engines.

    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router


  7. #31
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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Talk to Ahren, gave me some good info. Yes, the benchtop pro is their stiffest most accurate machine. 2'x2' with ball screws leads to a very sturdy machine. That said, they have folks running their big tables with detailed aluminium projects with no problem. For my space limitations, the benchtop makes the most sense as thats exactly what they were designed for.

    On a side note, just touched base with one of my old high school buddies I hadnt chatted with since Dec, on a random note we got talking about CNCs, he's buying their 5'x10' table soon.

    So yea, might just go in with him and get best of both worlds. Use of an awesome CNC without losing space in my garage

    Thanks all for the amazing help!!!



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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Awesome machine options, in the same boat here.



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    Default Re: CNCRP Benchtop Pro or Standard 2424

    Quote Originally Posted by ddurbs21 View Post
    Is there such thing as a VFD with 110V input that will run one of the Chinese 2.2kw water-cooled spindles?
    For what it's worth, I've been using this set for almost a year now with zero issues. I see others warned against it but I've had very good luck so far. Your mileage may vary.



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