New DIY build - design suggestions/ideas welcome

[zeeflyboy]

Cheers...

Yes I was thinking perhaps some sort of height adjustable rail system with a fairly shallow fixed-position dust shoe... need to scratch my head a bit about how best to do that.

[zeeflyboy]

Bit more time refining the new Z-Axis design.

I realised I needed the plate that slides down to be slightly slimmer than the unit as a whole, otherwise it would jam on the water/chip tray sides when in the lowered positions so tweaked that along with some more design details and seals, tramming plate etc.

[datac]

> Dual motor Y-axis due to increased weight of beefed up gantry and to allow automatic squaring

Confused on that statement... A "beefed up gantry" shouldn't be flexing enough to require a machine of that width to even remotely require or allow those motors to pull it "square" and subsequently run things "square".

I'd skip the dual motors, tie the lower part of the gantry together with a single cross member and use a single screw down the middle. The results will actually allow you to claim having a "beefed up gantry" because of the now boxed design, and you'll save money on all those extras you do not need.

[zeeflyboy]

If I did move to a single screw would it be worth bumping up to 20mm screw and a nema34 in your opinion? Concerned that the acceleration may suffer on a single nema 23

Another one of my motivations for the dual screw is that it would make it relatively simple to widen the machine some time down the road if I move somewhere that I can build a bigger man cave, simply by extending the gantry and cross members. Whether or not I will actually end up extending is another question though.

[ger21]

Depends on how fast you want it to accelerate.

[zeeflyboy]

I've been getting on ok with those motors and the current machine at 600mm/s/s (23.6ish inches) - that's the minimum I would like to maintain but would be nice to be able to increase that for 3D stuff perhaps

[A_Camera]

I've been getting on ok with those motors and the current machine at 600mm/s/s - would be nice to be able to maintain or even increase that

You should definitely be able to have that acceleration. I have direct driven ball screws (1605 and NEMA23 steppers) and accelerating at 700mm/s/s. I don't think that's the top for me, but don't bother with trying to find the maximum, it is fast enough as it is. In fact, I reduced from 10,000mm/min at 900mm/s/s to 8,000mm/min (Z only 7,000mm/min) at 700mm/s/s because I felt it was a bit too much and scary...

[zeeflyboy]

cheers - do you know how heavy your gantry/Z-axis/spindle is, and you are running from a single nema23?

[A_Camera]

cheers - do you know how heavy your gantry/Z-axis/spindle is, and you are running from a single nema23?

My Z is only about 8,5kg (plus spindle and cables). Here is some more data and some pictures:

https://adapting-camera.blogspot.se/...echanical.html

There are other posts on my blog as well. My CNC story is long...

Yes, only NEMA23 motors, but it is a fixed gantry type with moving table, so the X beam is pretty rigid made. I made some additional changes since I wrote the last post and the total weight is over 80kg. My machine is standing on it's own feet, but is table top size.

[mactec54]

Bit more time refining the new Z-Axis design.

I realised I needed the plate that slides down to be slightly slimmer than the unit as a whole, otherwise it would jam on the water/chip tray sides when in the lowered positions so tweaked that along with some more design details and seals, tramming plate etc.

Your bottom linear Bearings should be at the bottom of the housing, you then would have your design the same as I make them, this gives you maximum support closer to the job, you can pocket the SHCS or put them in from the back

[zeeflyboy]

Ah yeah ok, basically reducing the lever arm effectively

As long as the bottom of the plate stays above the bottom of the spindle chuck then that's a good plan - I'll slide the blocks down a bit and slide the tram plate up a touch.

What are the SHCS sorry?

Any thoughts on 40x200 for the gantry vs the current 40x160?

Acamera - nice machine. I guess one advantage of the fixed gantry is that it's always going to be easier to get good speed and accel, unfortunately I'd never fit a big enough machine for the work area I want going that route.


Edit - ah, socket head screws maybe?

[mactec54]

Ah yeah ok, basically reducing the lever arm effectively

As long as the bottom of the plate stays above the bottom of the spindle chuck then that's a good plan - I'll slide the blocks down a bit and slide the tram plate up a touch.

What are the SHCS sorry?

Any thoughts on 40x200 for the gantry vs the current 40x160?

Acamera - nice machine. I guess one advantage of the fixed gantry is that it's always going to be easier to get good speed and accel, unfortunately I'd never fit a big enough machine for the work area I want going that route.


Edit - ah, socket head screws maybe?

Yes that's correct socket head screws, or also call socket head cap screws, they nearly always are used in a pocket for this type of construction, like you have done in the top plate

Don't worry about speed and acceleration, your machine is not very big and will move as fast as your motors will start and stop, most machines never get up to there full commanded speed before they have to change direction or stop, you would need AC Servo's if you want max performance

For your gantry 40 x200 gives you more rail spread which is good but the part that is important is the 40mm thick, which is the weak point

[ger21]

Ah yeah ok, basically reducing the lever arm effectively

As long as the bottom of the plate stays above the bottom of the spindle chuck then that's a good plan - I'll slide the blocks down a bit and slide the tram plate up a touch.

Only move the bottom blocks down, if possible. The farther apart the blocks are, the better.

[A_Camera]

Don't worry about speed and acceleration, your machine is not very big and will move as fast as your motors will start and stop, most machines never get up to there full commanded speed before they have to change direction or stop, you would need AC Servo's if you want max performance

OK, I admit, I don't know MOST machines, but I am pretty sure you are wrong about this. Unless the acceleration is painfully slow, most machines SHOULD reach maximum speed long before they reach from one end to the other. Of course, for really high speed and acceleration you need servos, but that is overkill for small machines.

Here are my values:



Uniform accelerated motion (acceleration) Calculator - High accuracy calculation

It takes 12mm (0.5") to get up to maximum speed, so,every time I move more than that I am at 8000mm/min. Even if I had a slower machine I'd reach maximum speed pretty fast, for example a machine with 5000mm/min maximum speed and 500mm/s/s acceleration reaches maximum speed after about 7mm, so indeed speed and acceleration are important even in small machines. Acceleration is in fact even more important, since most of the time we are not moving long but accelerate many times small distances. This is the case regardless of machine size.

[A_Camera]

Acamera - nice machine. I guess one advantage of the fixed gantry is that it's always going to be easier to get good speed and accel, unfortunately I'd never fit a big enough machine for the work area I want going that route.

Thanks. Higher possible speeds and acceleration is one advantage. The other is rigidity, it is easier to make it more rigid than moving gantry type. The third is squaring. That is CONSIDERABLY easier to do on a fixed gantry machine. The fourth is less vibrations. Less moving parts makes it also easier to build. There may be other advantages as well, I don't know, but basically I think there is just one disadvantage, that is what you mentioned, it takes about 1/3 more space for the same milling area.

Yes, I use socket head screws wherever possible. I like them more than other type and don't mind if the heads are visible.

[datac]

I see that you have altered your Z axis design from moving bearings to moving rails.

That's all fine, as long as you fully realize the advantages and/or limitations to each. One limitation to moving bearing happens to be usable travel. One disadvantage to moving rail is when/if you would be required to insert a uniquely long tool into your chuck, and now when the Z axis is all the way up, still hangs down measurably into your work area.

Both are uniquely different, both have their good and bad points depending on what you will be doing. Imagine having only 6" of clearance under your gantry, and a 4" long tool that hangs down into that 6" area. No matter how you slice it, you can not use any more than 2" of the bottom of that tool. So, if a future goal is foam plugs or deep 3d models, make sure you have accounted for the height of them and total space under the tooling rather than just the chuck alone.

I've built them both ways, depending on actual needs. With your last direction, make sure you just rethink what your under gantry clearance will be given the above difference.

[mactec54]

I see that you have altered your Z axis design from moving bearings to moving rails.

That's all fine, as long as you fully realize the advantages and/or limitations to each. One limitation to moving bearing happens to be usable travel. One disadvantage to moving rail is when/if you would be required to insert a uniquely long tool into your chuck, and now when the Z axis is all the way up, still hangs down measurably into your work area.

Both are uniquely different, both have their good and bad points depending on what you will be doing. Imagine having only 6" of clearance under your gantry, and a 4" long tool that hangs down into that 6" area. No matter how you slice it, you can not use any more than 2" of the bottom of that tool. So, if a future goal is foam plugs or deep 3d models, make sure you have accounted for the height of them and total space under the tooling rather than just the chuck alone.

I've built them both ways, depending on actual needs. With your last direction, make sure you just rethink what your under gantry clearance will be given the above difference.

Your under gantry clearance is the same no matter, what way you make it, that part does not change, the lowest point is the bottom of the main Housing, the moving rail is a superior design in this case than fixed rail, this design can help to have more under gantry clearance

[mactec54]

OK, I admit, I don't know MOST machines, but I am pretty sure you are wrong about this. Unless the acceleration is painfully slow, most machines SHOULD reach maximum speed long before they reach from one end to the other. Of course, for really high speed and acceleration you need servos, but that is overkill for small machines.

Here are my values:



Uniform accelerated motion (acceleration) Calculator - High accuracy calculation

It takes 12mm (0.5") to get up to maximum speed, so,every time I move more than that I am at 8000mm/min. Even if I had a slower machine I'd reach maximum speed pretty fast, for example a machine with 5000mm/min maximum speed and 500mm/s/s acceleration reaches maximum speed after about 7mm, so indeed speed and acceleration are important even in small machines. Acceleration is in fact even more important, since most of the time we are not moving long but accelerate many times small distances. This is the case regardless of machine size.

In theory and calculation's that is correct, let's see it in practice, on these small machines, and then stop once it reached the12mm move at 8000mm/min ( 315" /min ) with a stepper

Servos are for any size machine

The only difference is if you want to pay the extra for them, there is no disadvantage what so ever having a quality servo for a small machine, just lots of Pluses

[wizard]

Thanks. Higher possible speeds and acceleration is one advantage. The other is rigidity, it is easier to make it more rigid than moving gantry type. The third is squaring. That is CONSIDERABLY easier to do on a fixed gantry machine. The fourth is less vibrations. Less moving parts makes it also easier to build. There may be other advantages as well, I don't know, but basically I think there is just one disadvantage, that is what you mentioned, it takes about 1/3 more space for the same milling area.

Yes, I use socket head screws wherever possible. I like them more than other type and don't mind if the heads are visible.

If somebody is building a small machine I see a moving table design as a hands down winner. There are lots of reasons some of which might be debatable some not so much. I might add to your list the following possible advantages:

1. More mass can be put into non moving parts of the machine thus damping vibration and possibly addit to rigidity.
2. That mass can be added by filling tubeular steel with anything from lead to epoxy concrete.
3. There are fewer electrical lines that need to move and flex. This can be huge in that it allows cost reductuion through elminated or downgraded parts. You only have one axis that needs its wiring running thorugh a drag chain or something similar.
4. It is farily easy to enclose such machines. This can help greatly with chip control and coolant control.
5. You end up able to acheive a higher degree of precision in machine alighment which can be huge for a small machine. You mention this in your response but i think people under estimate how much of a postibve this can be. You can literally achive milling machine like results given a good stiff gantry design. Certianly good enough to do prcision milling on aluminum and possibly other materials with lower speed spindles.
6. The gantry. base and other parts of the mahcine not in motion can be braced in any manner you want leading to very stiff mechanical designs. This can lead to machine that are easy to move about and set up with minmal effort. If I wanted a portable machine, say somehtign ot take to a job site, a moving gantry machine would be high on the list of acceptalbe designs.
7. The biggest problem with moving table designs is that some parts of the table might be unreachable which some will see as wasted space. Howver if you look at the very common knee mill, many bed mills and so forth you can see that this isn't uncommon in the mahcining world. The machinist just needs to be able to adapt to the hardware and use it to his advantage when creating fixturing and so forth.
8. This probalby applies to small machines more gnerally but a small frame can be easily mounted in a milling machine of a size that is ocmmon in many shops around the country. This means that mouning pads for bearigns or the gantry can be machined to a high precision with relative ease. In other words it doesn't have to cost an arm and leg to get your frame machined in a machine shop. Obviously lhis applies to moving gantry machines also but you still have issues with keepign the gantry square in operation on a moving gantry design.
9. From the human factors standpoint it is easier to keep track of what is going on at the cutter if the cutter is moving only on one axis.
10. Less money spent on "plumbing". This is ismialr ot the issues of elexctrical wiring in drag chains. Most of your plumbing can be with permanent hard plumbing instead of hose that wears out. hoses are subject to the same failures in drag chains as electrical wiring so being albe to minimiz how much hose ahs to go through such flexing saves you money in the long run.
11. Speaking of hose, your larger hoses such as vacuum hoses for dust collection, can be dropped from the ceiling down to the Z axis on the gantry. Since the gantry doesn't move and the Y axis stroke is mimimal the hose can be easily hung in such a way that the movements are easily handled even from a relativley low ceiling. In other words a moving table design mimimizes the horrors of handling the vacuum hose for chip collection. Many appaorches are viable that might not work well on a large moving table machine.

[datac]

Your under gantry clearance is the same no matter, what way you make it, that part does not change, the lowest point is the bottom of the main Housing,.....

Perhaps you misunderstood me. Sure, the gantry clearance is whatever you want to make it. In his design, TOOLING will infringe on that space.

This is important for the OP to stop and think about because he is coming from his old machine, where he has always been able to fully retract his tooling from the gantry clearance, making that distance always 100% guaranteed. The new design will no longer allow that and very likely will already require an increase in his current clearance, unless of course, he changes his Z axis again to allow the lowest part of the z axis plate to rise higher than the gantry clearance by the dimension of his longest intended tooling.

If the goal is to cut nothing but PC boards.... well, then this is a non-issue.

A usable Z axis design must work hand in hand with available gantry clearance, or, the longest bit will quickly minimize the maximum height of an object that can be machined, and/or, the shortest bit will not even reach the table plane when in full down Z location.

And, I use "tooling" loosely.... these days, one can venture into things far beyond cutting tools, from hot foil work, hot foam cutting, liquid dispensing, pick and place, stamping, metal punching/forming...... the list goes on. Design must target intention, but should also include at least a little headroom for other potential.

Regards one method being Superior over the other ? I disagree...... EACH has its own advantages and disadvantages, and which to use really comes down to actual end goals, and also why OEM machines continue use each design rather effectively. That said, I have built far more machines with the moving rails than bearings, but take all things into consideration, especially that of "under tooling clearance".