Finally building a 4x8

[SScnc]

I'm about ready to start welding steel. I haven't purchased the steel yet but expect to on Monday 6/21/21 so still time to recommend any design change. This is my 4x8 design and I plan to use the following....

Avid CNC rack and pinion drives and gear racks,

Linear rails on all axis (looking for about 2800mm lengths ?)

I plan to order a Z axis assembly from Amazon to save time.

Nema 34's with drivers from Stepperonline (48 volt) with seperate PS's for each Driver

I have the gantry too high in this design pictured and will be modifying it to lower it. The gantry will also be 2x6x.25 steel.

I've always used Mach3 but my laser has a DSP on it and I really like it. So I'm thinking of going that route with this CNC router, if I could get recommendations on which DSP would be good please.

Any suggestions/improvements or criticisms are very welcome please.

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[pippin88]

My advice is don't buy anything yet.


Comments:
Your gantry uprights are flimsy

Need diagonal bracing for the table.

Add another set of legs in the middle (why have such a long unsupported span?)

[routalot]

I agree with the advice in post #2 and would add that a triangular brace from the overhanging ends of the gantry beam to the bottom of the upright will be a useful addition.There is no such thing as a machine that has too much stiffness.

[peteeng]

Hi SS - How are you going to get the rails parallel? Welding a frame like that means the steel bench rails will not be parallel? Also probably will be wavy due to the crossmember welds...I would not weld the members "all round" only weld on the sides that induce the least warpage. Peter

[SScnc]

Thanks for the replies. The gantry uprights are designed as 1" thick aluminum plate with 3/4" aluminum rectangle bolt on to them at 90 deg. They do look flimsy in those pics, I'll post better ones showing more detail. And they are too high, I plan to reduce their height by about half. There is also a rectangular plate on top of both of these that the gantry bolts to.

I agree about the diagonals and will add them. The side rails are 2x6x 0,25 and really heavy, with adding diagonals coming from low on the legs up towards the center of the 2x6 side rails I hope center legs aren't needed. I've learned over many years how to weld with the least amount of warping.

I think with accurate cutting of the 2x2 cross members between the rails along with proper welding methods (not welding all around as you say, until all are partially and correctly welded in place) I believe I can get them parallel. However, maybe I should weld on some 1.5" wide "shelves" at 90 deg to the side rails then set my linear bearing rails on them with gear rack under. Then I should be able to get the linear rails parallel with some adjusting. (?)

All valid points and I will give these things more thought.

For the linear bearings, I'm looking at automation-overstock for their BLH ones, any thoughts ?

And should I continue to use Mach3 (I have several old PC's available) or something else ?

[machinedude]

Hi SS - How are you going to get the rails parallel? Welding a frame like that means the steel bench rails will not be parallel? Also probably will be wavy due to the crossmember welds...I would not weld the members "all round" only weld on the sides that induce the least warpage. Peter

a little extra length on the side rails won't hurt. i used 2900mm long rails on mine and ended up with around 100 inches of travel. you will want a little bit beyond 96 inches of travel for tooling travel to deal with a full sheet. and a wide stance on the bearing trucks will add stability to the gantry

machining the cross sections on the upper frame will go a long way keeping things parallel with the rails, welding will cause things to move and the tube itself is not going to be straight but you can also use shim stock to compensate for distortion to correct things.

the best way to deal with all this is to get the frame machined for the two datum points that control the parallel setting of the rails and the flatness in relation to the table top. but this is not that common for home builds since the cost of finding a shop with big enough machines to do this is not cheap. you also have the added cost of moving a large weldment from build site to machine shop and then back to the build site. you can see how the cost adds up going this route.

i would spend as much time as it takes getting things squared as good as possible. it will save you a bunch of headaches later on. i would look into the wire under tension method of setting rails to deal with the sage and wave in the frame when you start getting into setting rails if you are looking for the cheapest way to get things close. cheap is not always easy but it can make things a lot better.

before you weld anything taking something like music wire, fishing line or anything else than can take tension and is light weight and stinging it across the tubing this will be a quick indicator of how tube is not straight from the start. once you get things welded up this will show you the high and low spots of the frame in general so you can correct things. good luck in advance it's a real treat doing things on the cheap side if you go this route

[SScnc]

Right on the length, I have it designed at 108" now. So I plan to order 2800mm linear bearings, probably 20mm or 25mm ones.

GREAT idea on the music wire ! I'll do that, thanks ! And yes, I'm real big on getting things square, level and straight and will take as long as needed to do so.

[machinedude]

i have seen some other methods of getting things set with machine setting compound as well. it just depends on how you want to go about the support under the rails. the machine setting compounds i seen were metal filled so they are made for the task at hand. have seen some use a copper wire and this compound. if you have something that can be indicated easy then this might be a good choice in some applications. the copper wire acts like a support while you indicate things in and as you tighten the bolts the copper will crush to create some adjustment and hold things in place while the the leveling compound sets, once it is set i think you can go back and torque things down but i have never used it myself just something i have come across in my own problem solving.

[SScnc]

i have seen some other methods of getting things set with machine setting compound as well. it just depends on how you want to go about the support under the rails. the machine setting compounds i seen were metal filled so they are made for the task at hand. have seen some use a copper wire and this compound. if you have something that can be indicated easy then this might be a good choice in some applications. the copper wire acts like a support while you indicate things in and as you tighten the bolts the copper will crush to create some adjustment and hold things in place while the the leveling compound sets, once it is set i think you can go back and torque things down but i have never used it myself just something i have come across in my own problem solving.

More great ideas that I hadn't thought of, thanks and please keep'em coming !

[machinedude]

More great ideas that I hadn't thought of, thanks and please keep'em coming !

with the tensioned wire method spend around $100 and get yourself a digital microscope it will be worth the extra money so you can see the wire gap along your rails. the magnification is good enough to see .001 to .003 gap between the wire and rails. this is very helpful getting the table flat with your side rail configuration. you need a good 3 foot straight edge and a .001 to .002 feeler gauge to check for flatness over a large distance.

all the information i seen for the tensioned wire method made use of a loupe to help see things better the digital microscope has far better magnification and is a better choice.

[Dean448]

I have a DSP on a laser and agree that it runs smoothly. I also would like to see that for routers. 3D printers also have good control that doesn’t require a PC. Duet3d for example.
Routers require more operator interaction resulting in more complexity. There are non pc controllers but you have to be ok with how they operate. Acorn CNC is one example. Or Masso. Bit more pricy.
PC control is pretty efficient and low cost. Mach3 is ok with old operating systems where Mach4 runs on Win10. Btw there is a lower cost range called Grbl that uses open source software.


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[SScnc]

I have a DSP on a laser and agree that it runs smoothly. I also would like to see that for routers. 3D printers also have good control that doesn’t require a PC. Duet3d for example.
Routers require more operator interaction resulting in more complexity. There are non pc controllers but you have to be ok with how they operate. Acorn CNC is one example. Or Masso. Bit more pricy.
PC control is pretty efficient and low cost. Mach3 is ok with old operating systems where Mach4 runs on Win10. Btw there is a lower cost range called Grbl that uses open source software.

Well with that said, and since I already have several older very good PC's, and have used Mach3 for years on an X2 CNC mill as well as my previous CNC router with zero issues that couldn't be overcome, I'll stick with Mach3 until I find something worth changing to. Thanks !

[SScnc]

I'm trying to select a spindle for this build.

Any opinions on this https://www.amazon.com/Spindle-RATTM...8W51F8BG&psc=1 VFD Spindle combo ?

[Dean448]

Can’t comment on this specific unit. I think you should consider water cooled. By using water I think it’s quieter and doesn’t blow dust around. You just need a small water pump without a lot cooling.
Normal wood routers blow dust all over the place, I don’t know anything about this unit.


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[SScnc]

Can’t comment on this specific unit. I think you should consider water cooled. By using water I think it’s quieter and doesn’t blow dust around. You just need a small water pump without a lot cooling.
Normal wood routers blow dust all over the place, I don’t know anything about this unit.


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Good points, I care about both of those, and the quieter the better. I was avoiding the water cooled type just because of the additional pump, lines and tank but that's really not a big deal to get quiet, cleaner operation. Thanks !

[Dean448]

I use a CW3000 which is perfect for spindles. It has an alarm that kills the spindle if anything happens. Could use a pump and closed bucket but it won’t have an alarm.


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[peteeng]

HI SS - the spindle comes down to what you want to cut and how fast you want to cut it. If you only want to cut timber and plastic then 2.2kW is overkill unless you need the power to cut at high feed rates. A 1.5kW is much smaller and lighter and will do the job. The ER20 is used for 1/2" bits, if you never use 1/2" bits then use a smaller ER16 and it gets into tighter corners so depends on what you need it to do. I do deep bowls and moulds so need small collet nuts for instance to get deep on steep bowl walls. I'd rather have the lightest spindle at the end of the machine as I can... Peter

[jckstrthmghty]

I wouldn't worry about how loud the spindle is. The cutter on wood will be much louder. Much. I run an air cooled spindle and it doesn't seem to make "extra" dust.

[SScnc]

That's all good helpful info. I decided to go with a 1.5k water cooled, ER20 and VFD.

I ordered 9'-2" (2800mm) of 20mm linear rails for the Y and 5'-6" (1676mm) 20mm for the X from Automation Overstock with 8 medium preload bearing blocks. I emailed them with a couple of questions and in less than 24 hours Kent from Automation Overstock called me and answered all my questions and he recommended how to save on shipping.

Thank you all for the help ! I'll post pics as I get it built.

[mactec54]

I use a CW3000 which is perfect for spindles. It has an alarm that kills the spindle if anything happens. Could use a pump and closed bucket but it won’t have an alarm.


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Any VFD drive can shut down a spindle or motor if there is a problem