pros and cons of reducing gantry height?


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    Default pros and cons of reducing gantry height?

    Trying to reduce vibration when cutting steel as described here
    https://www.cnczone.com/forums/chine...el-router.html

    I already reduced vibration by reducing the distance from tool tip to bottom of Z brace from 12 to 4.5cm. Next, I was thinking of reducing the gantry height (with X & Z axes) by cutting off part of the 2 legs:

    pros and cons of reducing gantry height?-s-l1600-jpg
    I don't know how much this will help. I suspect little since the gantry looks very solid already. I also listened if cutting in the X direction is louder or softer than in Y direction, but didn't hear any difference.


    It seems the main operation I would no longer be able to do is lower the spindle to cut inside another valley/pocket. But how common is this operation? It doesn't seem that useful to me since usually you want to cut a pocket all the way through the material and for that, you can't rely on lowering the spindle, only by using long end mills.

    pros and cons of reducing gantry height?-delete-jpg


    Any other pros/cons?

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    Attached Thumbnails Attached Thumbnails pros and cons of reducing gantry height?-s-l1600-jpg   pros and cons of reducing gantry height?-pocket_inside_deep_pocket-jpg   pros and cons of reducing gantry height?-delete-jpg  


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    Default Re: pros and cons of reducing gantry height?

    The only con is you lose Z or gantry clearance. But I don't know if you'll see much benefit either.

    Gerry

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    Default Re: pros and cons of reducing gantry height?

    Well I just played your video and all I can say is you cannot put too much depth cut on a 3040, it`s not designed to do such ridiculous depth cut, it can just work on cutting mild steel with a maximum of 1mm depth cut on my experience on a 3040, so if you want to cut steel on it let`s say for example 20 mm thick, you need to program your route path in multi pass, 1 mm in each pass so that`s a total of 20 passes for a 20 mm steel cut, repeatability is the key when using a flimsy gantry type CNC 3040, shortening the gantry bracket will just limit your machine`s capability to work with thicker materials, master programming a multi pass method, go full speed on the XYZ and the spindle, you`ll be amazed how fast it can cut without modifying anything, think of it as an angle grinder in your hand, you dont need too much torque applied in your hand right? now you apply that method on your existing CNC 3040 and you`ll be happy with the results

    Also master sharpening your own tool bits, it will "REALLY" help you a lot on cutting harder materials, as much as possible stay away from HSS tool bits, your router spindle works very efficiently on the peak of it`s RPM range which is 24K RPM and no HSS tool bit can withstand that, only the carbide bits. I can cut steel on our CNC 3040 all year long without vibrations at all whatsoever



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    Default Re: pros and cons of reducing gantry height?

    go full speed on the XYZ and the spindle

    That's insane - you could use it as a friction welder! Even if the bits don't melt, Cracking from thermal stress could be a serious problem.

    Assuming the brute force way works and I don't need to reduce gantry height, then my problem is how to deal with the greatly increased distance (10cm) from tool tip to bed (I moved the spindle up in its brace to reduce vibration)? I can't find any clamps that can go that high. So that was the other motivation for reducing gantry height.

    work on cutting mild steel with a maximum of 1mm depth cut
    yes, I've figured that out the hard way after snapping several end mills



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    Default Re: pros and cons of reducing gantry height?

    I found this excellent article describing the forces at play in my type of router.

    Do it yourself CNC router: Design Considerations, the Gantry

    According to that source, when I reduced D1 by moving the spindle up in its clamp, not only does it reduce the torque on the X axis (moment A), but also reduces the torque on the poor Y axis (moment B). So there would be less incentive for reducing gantry height (D2).

    What I really need is a variable height gantry! Most of the time, it will have a low height for more rigidity. And rarely, I could raise it to do some wood relief carvings. CNC routers are already arguably the most versatile tool (can saw, drill, sand). Maybe this can give it enough rigidity to do milling.



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    Default Re: pros and cons of reducing gantry height?

    Quote Originally Posted by spacesaver View Post

    That's insane - you could use it as a friction welder! Even if the bits don't melt, Cracking from thermal stress could be a serious problem.

    Assuming the brute force way works and I don't need to reduce gantry height, then my problem is how to deal with the greatly increased distance (10cm) from tool tip to bed (I moved the spindle up in its brace to reduce vibration)? I can't find any clamps that can go that high. So that was the other motivation for reducing gantry height.


    yes, I've figured that out the hard way after snapping several end mills

    Well on my side, I always use a low profile vise clamp bolted on the table when working with metals, so the gantry height is so important to me, it does`nt really matter even if you shorten the gantry brackets due to the fact that your spindle is a 24K RPM, and it is designed to cut metals on a multi pass process, as for bolting process, you can always use longer bolts to do this, I remember the last time I profile cut aluminum material for a motorcycle and it`s as high as 60 mm using only 1/8 carbide straight tool bit, custom sharpened into a single flute, what I did was I literally bolted the material on the table hehe



    pros and cons of reducing gantry height?-20170228_104103-jpg

    Custom motorcycle parts 60 mm height profile cut directly bolted on the table. as you can see the 1/8 carbide tool bit is 90 mm long, it needs custom sharpening for you cannot buy directly a very long tool bits.

    pros and cons of reducing gantry height?-20170801_100323-jpg

    Custom gun parts clamped on a bench vise

    pros and cons of reducing gantry height?-20171102_074532-jpg

    Large Generator Stator Bracket aircraft aluminum 45 mm thick being cut by a 2 flute 8mm carbide for wood, custom sharpened of course.

    Honestly I have a lot of pictures being on products being made on a CNC 3040 800 watt spindle, I just dont wanna post it for security reasons

    I just want to show you how highly capable your machine is, modify the wiring harness maybe yes, it`ll add more torque on the steppers (XYZ)

    Attached Thumbnails Attached Thumbnails pros and cons of reducing gantry height?-20170228_104103-jpg   pros and cons of reducing gantry height?-20170801_100323-jpg   pros and cons of reducing gantry height?-20171102_074532-jpg  


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    Default Re: pros and cons of reducing gantry height?

    I've thought of a way to allow variable gantry height. I would cut slots in the 2 side walls (red) and brackets (green). Then clamp the red to the green with screws. When fully retracted, it would look like this
    pros and cons of reducing gantry height?-retracted-png

    The red will also be bolted to the base for extra rigidity against forces parallel to gantry (like in original design). When extended, it will look like this
    pros and cons of reducing gantry height?-extended-png
    This will be weaker against forces along gantry, but since this is only intended for cutting soft material (e.g. wood relief carvings), it shouldn't matter that much.

    I might be over estimating the importance of gantry height on rigidity. The flex from unsupported rails can also be a big problem as several people point out here
    https://www.cnczone.com/forums/diy-c...-rigidity.html

    Thoughts?


    KH0UJ, the parts I'm cutting are < 1cm thick, so I have to raise them a lot to reach the spindle. I tried using 10cm M6 bolts for clamping to several wood boards, but it keeps slipping. I will get a milling vise soon, but that will still involve raising the work by > 5cm, which can't be good for rigidity.
    BTW, I don't have much space for tools (living in San Francisco bay area), so it's reassuring you say that this machine which most people dismiss as a wood router is capable of cutting steel.




    Attached Thumbnails Attached Thumbnails pros and cons of reducing gantry height?-extended-png   pros and cons of reducing gantry height?-retracted-png  


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    Default Re: pros and cons of reducing gantry height?

    I really dont understand why you need to raise the gantry bracket, 1cm is only 10mm, on my case I can cut as much as 60mm (6cm) with the same gantry height as yours, if you really need to raise the gantry there`s a very simple way to do it, just replace the allen bolts holding the bracket with a longer ones, you can raise it as much as 50mm (5cm) by just using plain washers, I tried it on our units with no visible weakness on the gantry, just tighten it well to maintain it`s rigidity. and also if you need more height you can adjust the spindle holder until it`s just 3/4 of the spindle being clamped.

    Edit: if you look closer on the second picture I uploaded on your thread I only clamped the spindle 3/4 because I was working on thicker the material before I worked on the second part the one on the picture and I was lazy enough to re seat the spindle to it`s original position.

    Last edited by KH0UJ; 05-24-2018 at 08:38 AM.


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    Default Re: pros and cons of reducing gantry height?

    I think he wants to lower it to make it more rigid.

    Gerry

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    Default Re: pros and cons of reducing gantry height?

    Quote Originally Posted by ger21 View Post
    I think he wants to lower it to make it more rigid.
    OK boss but one question remains, why is it that I can do it without modifying anything on the gantry? and more tougher materials too.
    so basically he just need to change his CAM procedure to make it work I guess.



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    Default Re: pros and cons of reducing gantry height?

    He's trying to cut much deeper, with much higher chip loads than you do.

    Gerry

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    Default Re: pros and cons of reducing gantry height?

    Well on my experience on a CNC 3040, anything much deeper cut pass above 1 mm the the 2 rails on the X axis and the ball screw on it will flex causing a huge amount on vibration, you can even notice it by just wiggling the spindle back and fourth by hand, not the gantry bracket, modifying it to a bigger linear rail will be a nice approach than lower the gantry bracket on my opinion to my laziness on modifying the machine to have a bigger rails I just reposition the location of the material to the lower left or lower right corners of the table to avoid excessive vibrations, program the code with multi pass, if he tries to cut much deeper pass he needs to go slower on the movement (XYZ) while in multi pass he can speed up the movement over all and all in all the work time will be just the same but a happier tool bit (not stressed)



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    Default Re: pros and cons of reducing gantry height?

    I really dont understand why you need to raise the gantry bracket
    I'm lowering. The "raised"/extended position in the model is just the original height

    If I wasn't clear, my main motivation right now for lowering gantry height is so that the tool tip can reach the work without so much stacking. I decreased the slop between the tool and the bottom of the spindle brace from 12 to 4.5cm, which seemed to reduce vibration by 1/2. But that greatly increased the amount I needed to raise my flat iron work piece.
    I was then able to mill a few passes of my flux concentrator (to make magnets super strong in 1 direction) with relatively smooth finish (0.5mm depth, 200mm/min, 4000 RPM, 3mm HSS bit), until those flimsy M6 bolt clamps slipped. So it seems vibration is no longer the main problem.
    pros and cons of reducing gantry height?-reduce_slop-jpg
    pros and cons of reducing gantry height?-flux_concentrator-jpg

    Attached Thumbnails Attached Thumbnails pros and cons of reducing gantry height?-reduce_slop-jpg   pros and cons of reducing gantry height?-flux_concentrator-jpg  
    Last edited by spacesaver; 05-25-2018 at 05:41 AM.


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    Default Re: pros and cons of reducing gantry height?

    If I were you, I'd make two new side plates, as short as you need, and install those and would test it. Those plates can be ready for use after an hour or two work, so it is not a huge and difficult change. Assuming you have a saw and a bench/pilar drill, it is easy, unless you want some fancy milled version, but even that is possible, since you obviously have a CNC.

    ...on the other hand...

    I would not use wood as vise support. If the vise needs to be raised it is better to use something more stable, like aluminium. It would reduce vibration and increase the rigidity. So, as step one, I'd make a steel or aluminium box and fix the vise on that. Perhaps that solves all the problems you have without offering Z clearance, which you might need later. Even if it is pretty easy to replace the side plates, once done, you will need to square the machine, and must square it every time you change them. This goes also for the proposal you came up with, which in fact is pretty complicated and may not even be practical.

    ...but...

    I would also not use that vise, would buy a better one which is made for CNC works, not angle grinder/drill works. A good quality vise is necessary, especially if you are working with metal or require high precision.

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    Default Re: pros and cons of reducing gantry height?

    So you have a table vice then, on my opinion you can bolt it directly on the table for rigidity, to tell you honestly you can burn your spindle on that speed, it`s not designed to run on that RPM range, unless it`s a 12K spindle, but it`s not, it`s a 24K rpm spindle, you can also ask my boss (Ger21) about your spindle, you can use a single flute carbide tool bit and and crank your speed @ 24K RPM, you can cut on it efficiently, you dont need to reseat your positioning on your spindle, probably you got a lot of vibrations due to the fact that your spindle lacks torque, it will massively drop it`s RPM because it`s not designed to operate on that RPM range, I have done a lot of 3D molds on a steel material not just outlining job, I can cut all day on steel materials without changing a tool bit at all, and I operate the spindle full speed (24K) because that`s where the optimum torque on the spindle if it`s a 24K motor.

    pros and cons of reducing gantry height?-20161229_161709-jpg

    pros and cons of reducing gantry height?-20161229_161435-jpg

    These are my sample 3D cut molds, I cannot post any other output because I might get caught hehe (Dangerous Products if you know what I mean)
    I also have 10 years of experience on manual machining (Lathe & Mill), that`s why im a bit familiar on working on metals

    Attached Thumbnails Attached Thumbnails pros and cons of reducing gantry height?-20161229_161709-jpg   pros and cons of reducing gantry height?-20161229_161435-jpg  


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    Default Re: pros and cons of reducing gantry height?

    Is it just me, or there is too much expectation from a 3040 ?



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pros and cons of reducing gantry height?

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