[ishi]

Here are more details about the servo motor brackets that we are planning to use:

https://www.syk.tw/product/201703030006

They might require some additional machining of our granite base in order to provide a recess for the bottom flange though.

[ishi]

Catching up with a few comments I have. We use THK pre-loaded rails at work, we use from 20mm to 60mm. They are extremely well made, we have tried other suppliers but we have a very small tolerance, and the THK's are always well within our tolerance. It's very rare that we have to send one back, and when we do it's usually due to damage in shipping.

Same with the ball screw We use THK's and they are always good. We use very few that are under 40mm though. It's generally cheaper to use a linear motor on the smaller parts.

For positioning we use both encoders and glass scales, using scales on an axis feeds back actual position, reading encoder pulses is theoretical position (An encoder only reads how much a motor turned and does not take into account play in a system)

You are hoping your design will be built by others, because you see that something is missing. At the price point you are talking about I would guess 99.9% of the people building this would be commercial companies. And they most likely wouldn't do it simply because of OSHA, and the headaches involved. Also every manufacturing companies I've worked at's biggest expense is time. If they need it they need it to make a product to make money. Paying someone to build a machine when they can buy one doesn't make sense (even though the machine they need may have a 6 month lead time).

We make machines that make parts for something the size of a matchbox car to parts used in container ships. But we have holes in our product line, not because we can't make the machines, we would if ordered, but there is simply no market. I think the reason no machine like yours exists is because very few people need the precision your machine will be capable of for products the size yours will make. They can just buy a HAAS, that comes with a warranty, has a proven design and can be running in a few weeks.

And I don't mean to sound rude, but to think that your first machine design will be good enough to be used in a production environment is very hopeful. For a machine this size to be commercially viable you would plan on 5-10 people working for 2-3 years before it's ready for market. For one person to do this in their garage with internet help, you should plan on about 10 years, and at least one complete redesign. If my goal was to make this something others would use I would have to be ready to turn my $10k of granite into a garden planter.

TTalma,

I did some more research regarding linear encoders, and I am starting to think that they would make sense for my build. While the servo motors I am using come with absolute encoders, I'll get even more accuracy with linear encoders, and they're not as expensive as I expected them to be. They're not that cheap either (about $1,250 per axis), but in relation to the rest of the build, they make sense.

Right now, I'm looking at the ACU-RITE SENC 50:

https://machinetoolproducts.com/20-t...on-resolution/

3µm accuracy and 0.00002in resolution. Unfortunately, they're only available up to 20" travel. Beyond that, one must use the 150 line, which only provides 5µm accuracy:

https://machinetoolproducts.com/30-t...on-resolution/

For better accuracy (2µm), we could use the Heidenhain models:

https://machinetoolproducts.com/cate...near-encoders/

I'll try to get quotes for these as well.

I think it makes sense to factor that into the design, even if they're not installed initially. And it's likely that they would come as an option. But having them factored in the design from day one would avoid a costly redesign down the road, especially with respect to the necessary threaded inserts that would need to be added to the granite base.

If I could make a machine with 2µm accuracy, I would be pretty happy...

[ger21]

While the servo motors I am using come with absolute encoders, I'll get even more accuracy with linear encoders

No, you won't get more accuracy, you'll get more resolution, which you may or may not be able to use.

Once you get down to precision less than .001", you better have a climate controlled room, and then start thinking about how to keep the temperature of the screws from changing, as the length of the screws will change as they get warmer during use.
When you start chasing very high precision, things get far more complicated, very quickly.

[ishi]

No, you won't get more accuracy, you'll get more resolution, which you may or may not be able to use.

Once you get down to precision less than .001", you better have a climate controlled room, and then start thinking about how to keep the temperature of the screws from changing, as the length of the screws will change as they get warmer during use.
When you start chasing very high precision, things get far more complicated, very quickly.

ger21,

I do not understand that part. My assumption was that linear encoders would improve both resolution and accuracy, especially if the controller can properly take advantage of them. For example, they will help reduce the effect of backlash on the ball screw that absolute encoders in the servo motors could not take into account. Also, my understanding is that some controllers are able to mitigate (to a certain extent) ball screw length variations due to higher temperatures when using linear encoders. Did I get that wrong?

This article does a better job at explaining what I am talking about:

https://www.moldmakingtechnology.com...-part-accuracy

This "complete closed loop system" is what I am looking for.

That being said, I agree with you that climate control in the shop would help, and so would ball screw cooling. The former is totally independent of the machine. The latter would add too much cost and complexity, and I like to believe that a complete closed loop system will take my machine to the level that it needs to be, at least for version 1.0.

[ishi]

We've presented the project to one of the main suppliers of parts for the proposed build, and they're very interested by it. They validated the selection of a granite base for the build and will provide assistance both with engineering and supply chain. It's too early to name the partner, but it's the best we could have hoped for.

This little project just got a major boost... (^_^)

[ger21]

You're probably right, provided the controller can deal with everything.
But fixing any backlash in software can be problematic.

[ishi]

You're probably right, provided the controller can deal with everything.
But fixing any backlash in software can be problematic.

ger21,

You're absolutely right. Not much can be done regarding backlash, which is why I selected a "non-backlash" ball screw and am trying to get ball screws and linear blocks with as much pre-loading as possible. But I guess that the more pre-loading you get, the harder it gets to install the component, which means that we'll have to find the right balance.

[ishi]

I have outlined a set of design priorities, principles, and strategies on this document:

https://docs.google.com/spreadsheets...t#gid=41133701

I have also added a short introduction to the project there:

https://docs.google.com/spreadsheets...gid=1109769669

[ishi]

Technical information for all the components that we are planning to use have been put on a public drive:

https://drive.google.com/drive/u/1/f...Cl_E_6NK8kwBI-

The spreadsheet has been moved there as well in order to keep everything in one place:

https://docs.google.com/spreadsheets...gid=1109769669

[ishi]

For the touch probe and toolsetter, we could go with Blum or Renishaw. Both are great, but we'll go for Blum, because this is the supplier used by DamenCNC as well, and we trust their supplier selection criteria.

https://www.damencnc.com/products/cn...04_w_263__GB_1

We'll go for IR transmission in order to reduce the number of cables that need to be installed and make it easier to add more compatible tools down the line.

TC52 for the touch probe:

https://www.blum-novotest.com/en/pro...tc52-tc62.html

Z-Speed for the toolsetter:

https://www.blum-novotest.com/en/pro...ed-series.html

IC56 for the IR receiver:

https://www.blum-novotest.com/en/pro...ic56-ic57.html

All these will be optional, but we'll make sure to provide inserts on the granite base for the toolsetter and IR receiver. We'll also machine a cable conduit for the IR receiver.

[ishi]

The linear encoders we will use are the Heidenhain LC 495 S:

https://www.heidenhain.com/en_US/pro...-400-series-2/

DIADUR glass scale with absolute track and incremental track
±3 µm accuracy grade
0.001 µm measuring step
DRIVE-CLiQ interface

We will need them in 770mm, 520mm, and 270mm measuring lengths.

Still trying to confirm prices, but estimates have been included there:

https://docs.google.com/spreadsheets...SwA/edit#gid=0

Update: Final prices have been added. Not cheap, but the best components that I could find.

Also, we will install this compressed-air filter system: Heidenhain DA 400

https://www.heidenhain.com/fileadmin...A_02_DA400.pdf

This will help keep the linear encoders free of contaminants.

[ishi]

We've added and will maintain a list of open questions on our master spreadsheet:

https://docs.google.com/spreadsheets...gid=1415492304

[ishi]

While looking at the attached picture, I realized that we should install the electrical enclosures on the back of the girder, for multiple reasons:

1. There is plenty of unused space there: 48" x 24" × 12"
2. This would free up 40" × 20" × 12" of space in the underside table.
3. It would allow for much bigger enclosures.
4. It would be more ergonomic.
5. It would reduce cable lengths.
6. It would improve thermal dissipation.

The last point is the most important one: by installing the electrical enclosures in the underside table, we get heat dissipation toward the granite base, which is not good. But because hot air moves up, by moving the enclosures up toward the top of the machine, we will get hot air moving up away from the machine. Additionally, we could add a thin layer of reflective mylar on the back of the enclosure in order to reflect 98% of IR radiations away from the bridge.

The current plan is to use two of these 24" x 24" × 12" enclosures:

https://www.hammfg.com/part/EN4SD242412GY

This change will in turn leave us enough space to install the Unist Quantum lubrication system, instead of the Revolution model (both are approximately the same price):

CNC Machinery Lubrication System - Automatic Lubrication System - Quantum | Unist

The Quantum will make it easier to integrate with our controller and can be ordered with a remote control.

[ishi]

These instructions from Haas regarding the replacement of the tank and cylinder used for the Z-axis counterbalance on their VMC machines is quite helpful.

https://diy.haascnc.com/procedures/v...ce-replacement

[ishi]

We have added an outline of all electrical, pneumatic, and hydraulic (oil + water) circuits. 60 cables and hoses so far...

https://docs.google.com/spreadsheets...gid=1030513671

[rowbare]

I got a quote for the HSD spindle:

ES351 - H6161H1036

$12,400!

Gasp.

That being said, quality does not come cheap, and that price includes the encoder, which would allow me to do rigid tapping. On a high speed spindle (40,000 RPM), that would be really nice. Also, some suppliers tell me that I should be able to get it for much less than that, so I'll budget $10K for now and assume that we'll go with that model. Only problem: it usually takes 12 weeks to get. So, if I order everything by the end of the Summer, we won't get any chips before Christmas.

Well, here is our time table...

I don't see how you are going to do rigid tapping with a router spindle. Once you get down to rigid tapping speeds, you won't have a whole lot of power left. You might be able to rigid tap small thread sizes but you will be very limited.

bob

[ishi]

I don't see how you are going to do rigid tapping with a router spindle. Once you get down to rigid tapping speeds, you won't have a whole lot of power left. You might be able to rigid tap small thread sizes but you will be very limited.

bob

bob,

You're absolutely right, rigid tapping will be limited to relatively small thread sizes. For larger ones, I'll have to revert to thread milling.

[ishi]

I am sketching the cast iron boxes for the carriage and spindle assemblies, trying to make them as low-profile and rigid as possible. This is actually oddly satisfying. There is something almost "organic" about the casting process, and I'm really excited about that part of the project.

In doing so, I realized that I did not provide enough clearance for the ball screw assembly. Therefore, I have to go back to the drawing board and select different linear blocks. I also need to research how iron castings can be precision-machined, especially for the surfaces on which rails and blocks will be mounted. Some of the profiles that I have in mind for these castings might make this machining difficult or even impossible.

[ishi]

Here is a radical idea: what if the rails for the carriage (X axis) were mounted horizontally instead of vertically? I got the idea when looking at a vertical machining center from Hyundai (see attached picture). This would bring many benefits, among them:

1. Less deflection, because a single axis would be mounted vertically, instead of two.

2. Easier assembly, because the overhanging piece is much lighter.

3. 12" shorter machine height, because the girder's height could go from 24" to 12".

4. Perfectly balanced bridge (same weight from and back).

The main problem with that design is that you need a really rigid and perfectly square carriage assembly. But here is the radical part of the idea: what if the carriage was made out of granite as well? I know this sounds crazy, but think about it for a minute: we already know that we can get flat and square granite components, and granite is more rigid and stable than cast iron or weldments. The only problem is that it's heavy. But how heavy would it be? Well, it we made the carriage frame as a 16" x 16" x 24" block with a triangular profile and a wide cylindrical hole at the center of gravity of the triangle, it would be less than 250 lbs. Knowing that the spindle assembly will weigh at least 100 lbs, that does not sound crazy at all. And that means that we would have to cast a single piece (the spindle box).

I will try to sketch that up.

[ishi]

Here is a first sketch of what the carriage could look like. It would be made of two pieces of granite. The proportions and sizes are not right, but I wanted to get a sense of the total weight for the assembly. The triangle profile is about 154lbs, while the vertical plate on which the Z axis will sit is 112lbs. That means a total of 266lbs, or 121kg. I think it's totally acceptable. In fact, I'd be comfortable with up to 250kg.

Next, I'm going to play with dimensions and profiles. For example, the triangular profile should go all the way to the top of the plate in order to best support it, and it should not extend over the back of the girder so that we can still assemble the electrical enclosures on the back of the girder. This will make it difficult to perfectly balance the carriage alongside the Y axis without adding a ton of weight to it, but I don't think this should be a problem. I will also make the vertical plate as wide as the triangular profile in order to facilitate their squaring. With all these changes, the rails for the X axis should be 9" apart, while the ones for the Z axis a full 13" apart.

This should make for a very rigid carriage assembly.

But I still need to solve one major problem: how to mount the linear blocks for the X axis on the carriage assembly. Here is a tricky one!