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The Meticulous Z-Axis


#21

I propose a change. Mount the z-axis rails higher, in the z-direction, so that it doesn’t interfere with the linkage kit. In addition to making room for the hose, it would allow the router to push farther down, into the work. I see this being applicable in situations like this, in which there is potential need for deeper cutting capability.


#22

I’ve considered raising the rails myself. However, I’m not sure it would do everything you’re suggesting. In fact, I believe it would shorten the travel distance at the bottom:

This would especially be an issue for shorter bits, because they may not be able to contact the work surface or at the very least would have limited travel into the material. We’d need to test this before I implement it in the design.

If it does work, though, that would be nice, because we could widen the dust chute to increase airflow. It also means we could widen the distance between the rails, which would help with stability.


#23

You are right. I was thinking completely wrong. Let me try again.

Still move the z-axis rails up. Simultaneously, lower the router position relative to the z-axis bearings.
ZAxisUpdate


#24

Hey, I got the gear-sets backwards earlier. It happens.

That could work. I positioned the bearing block so that the screws would be accessible from the front side with the spindle clamps in place. I could move the block here:

and it would satisfy both of our criteria. :smiley: I might even remove the overhang at the bottom so it doesn’t get caught on the linkage. I like the change. Sometimes you get stuck when your designing something yourself.

Shouldn’t take me to long to make the changes. Not sure if I’ll have time tonight, though. It’s the wife’s birthday and I’m sure she wouldn’t be happy with me putting her off for Maslow stuff. Especially given that she’s a little frosty about how much development I’ve been doing and not making cool stuff for her/us.


#25

Great! I sympathize. You don’t want your wife frosty. If it is her birthday, you’d better be on your best behavior.


#26

One other thing. I think it is important to maintain a certain spacing between the bearing blocks. It may mean that you need to move the top bearing up, too.


#27

Well, I had a little bit of time at the end of my work day to make the changes. I still need to polish the design, but here is how it looks with the change:

Apparently with the block that high, the spindle lock will hit the dust hood window. We might want to look into limit switches! >.< I overestimated the amount of extra clearance we need.

The good news is we only lost 10mm of travel by relocating the blocks. I’m going to have to take some time to alter the dust hood chute. I’d also like to widen the back a little to give us some more stability. To do that, I’m going to have to lift the linear rails again to clear the linkage risers. Good thing I’ve got room to play with for the rail blocks.

There’s always time tomorrow :wink:


#28

Would it help if the community cut out some gifts for her?


#29

I was actually thinking about raising the z-axis high enough that it was higher than the linkage members. That would make a lot of room.

Additionally, we could consider increasing the span of the linkage, if necessary.

@jwolter, I like the way you think.


#30

Most certainly! I know she likes @bar’s drying rack, for our new kitchen. You guys are awesome!

I don’t want to raise the rails too much. The taller the axis gets, the higher the center of mass. Once I have the design a little more polished I’m going to have to do some mass simulations to figure out where it is right now. I could entirely be over-concerned with the axis height.


#31

We might want to understand the sensitivity here. I don’t think it is too sensitive; raising the z-axis by a few inches might raise the center of mass by 1/2 inch. Has anyone done analysis to understand the consequences of 1/2" of CG height? If not, I would like to test it before it is eliminated as an option.


#32

Another idea. We might be able to switch the motor to the bottom of the lead-screw. That would lower the CG a little.

Another thought. I am sorry for inundating you. Sometimes I cannot help it. I was thinking about the motor mount. In the current design, correct me if I am wrong, there is no ability to tighten or loosen the belt. This would be some kind of horizontally movable piece, a horizontal degree of freedom in the motor’s mounting position, so that the belt could be installed then tightened. This would take the form some horizontal slots that have a bolt or screw going through. In the current design, this is present in the vertical direction, due to the slots in the metal motor mount.


#33

To be clear, I’m not as worried about the extra weight of the plywood/linear rails. Those will have a very minimal effect on the center of mass. I massed the entire Z-Axis kit and it only came to 326 grams, or 11.5 oz (0.72lbs). My major concern is with the router. That masses almost 3kg (6.6 lbs), and when it’s at the top of the axis it will push our center of mass up significantly.

Personally, I don’t like mounting the Z-Axis motor at the bottom of the lead screw. That means we have to put a hole in the back and there isn’t a lot of clearance for a pulley down there. That’s not to say that it isn’t possible, more than I like the motor where it is.

In my model I’ve raised the linear rail mounting blocks 40mm from the original position and I think I’ve found a position I’m happy with. It’s tight, but not problematically so.

This is the view from behind the router, with the back hidden:

And this view is from in front of the router, with no parts hidden.

The first view shows us that the current configuration gives us a hard “stop” at the bottom of the axis, just before the router plunges through the dust hood window. I like having a hard stop there to prevent the machine from breaking a linkage member or the plexi window. I would also like to add a limit switch to add a soft stop just before it hits that hard stop, though. Does anyone know how difficult it would be to implement limit switches into the firmware? Luckily, the belt will most likely slip before something breaks, so we should have a good failsafe in case we hit the hard stop.

This is a good point and it’s something I’ve been thinking about on the back burner. Ultimately, yes, I would like to make up a bracket with horizontal adjustment rather than vertical. I drew in the bracket that comes with the kit for the prototype and until we have a more final version, I don’t think it’s worth putting the time into making up a separate bracket.

Also, the advantage of timing belts over a serpentine or v-belt is that it’s much less sensitive to tension. At least for the prototype, it should be relatively easy to screw the Z-Axis motor with the belt on it to tension it.


#34

This aligns very closely with my thinking. The modification I was suggesting would hold the motor z position constant. The rails, rail mounts, bearings, and lead screw would move up to make room. The bearings would contact the mounts at the appropriate location in the z-travel, to produce a hard stop. The z-axis carriage and Z-axis spine would have to be taller to accommodate.

I am wondering how much clearance has been created for the vacuum hose. I was originally hoping to create enough space for a 2.5" hose.

OK. You are right. It would be more complicated; bad idea from the start.

I have another idea. What if we make the 45 degree linkage into a 40 or 35 degree kit (closer to horizontal)? It would bring the kit mounts out and up. It could free up needed space. It is my understanding that the original decision of 45 degrees was not precise, so 40 or 35 could work just as well.

OK. Before the bracket is designed, we’ll just have to use spacers to make sure the motor is mounted and the belt is tight. Maybe I will create something temporary.


#35

the length of the rails is an easy thing to change, make the default have 3" or
so of travel and you will cover 90% of people, and the rest can use longer
rails.

realistically, some people will want a lot of travel to be able to use long
router bits.

Just point out the balance issue (This is why I argued for an adjustable top
beam, so that it can be moved out as far as needed to deal with this)


#36

the chains need to go from ~10 degrees to ~80 degrees, 45 is nice and in the
middle, so chain relative to the bar is ±35 degrees.

If you put them at a different angle, then you need to make sure that the chain
mount can handle the extra angle.


#37

Before we get too much further into dust collection, I’ve decided that it’s time to get some actual numbers on our requirements. I apologize in advance for the novel this post became. I’ve found this article from Wood magazine, which gives us a baseline. In particular, I’m looking at this section:

I’m going to work from the router table example, since it is probably closest to the Maslow. This would give us a required airflow of 195 CFM from the tool. This means that even a 2 1/2" hose is throttling the dust collection flow a little. A 3" hose would give us the required flow for the tool.

Side note: The Rigid R2200 has a 1 1/4" dust collection port on it. That means that either Rigid is expecting very little airflow is needed for the tool or they simply didn’t engineer the dust collection port correctly. I’d believe that its the latter, because when I use my router freehand dust gets everywhere, even with a shop vac connected.

So let’s get into the math. As far as calculating flow, I’m more interested in the rectangular calculations rather than the round ones since my chute’s interior is rectangular. The formula I’ve derived from the article is:

A = (W * H) * 28

Where:
A = Air flow in CFM
W = Interior Width in inches
H = Interior Height in inches

There is 68mm (2.677") currently between the inside faces of the linear rail blocks. We should probably factor at least 0.4mm (0.015") clearances between the rail mounts and the outside of the chute. We have to factor a 3mm wall thickness to get the inside. So the interior width of the chute as it is currently drawn is 61.2mm (2.409").

So:
A = (2.409 * 3) * 28
A = 7.227 * 28
A = 202.356 CFM

We need the section of the chute to be 61.2mm (2.409") x 76.2mm (3") consistently. The issue here is consistently.

Where the chute meets the hood body is really the issue. The opening starts at 113.49mm (4.468) wide, and is 15mm (0.59") tall. This gives us an airflow at this section of 74 CFM, which is less than half of what we’d need. I can’t make this part taller, which would be the easiest way to solve the problem. Right now, we have 8mm between the bottom face of the collet and the stock top. That is with the spindle lock mechanism against the dust hood window. In order to accommodate 1/8" tooling, the most I can comfortably push that is to 12mm. That would give us closer to 94 CFM, which is better, but not great.

The other option is to cut a relief in the top face of the sled to increase the height of the opening. Routing 1/2" into the face would give us 156 CFM, which gets us to the 2.5" requirement. That is factoring in the 4mm we gained by increasing the height of the dust hood. This adds a whole lot of complexity, though, because now the sled has to be machined on both sides for all the required features. I’m not sure if that would ultimately be asking too much of beginners.

This post has already gone on for too long, but I’d like to touch on another related issue:

I was able to look at the center of mass of the model. I had to make the HDPE pad on the bottom steel to approximate the weight correctly. I have the sled massed at 13.6kg, or just under 30 lbs. This is roughly where Fusion thinks the center of mass would be with the router at the bottom of the axis:

I’m definitely going to need to raise the linkages by at least 3/4", though I’m thinking that 1" might be safer. This is going to make it hard to move the linear rails to be over the linkages and still have the router be able to plunge through a sheet of material.

I could probably keep this going but I’m going to end this here.

The TL:DR here is that I’m going to have to do at least some redesigning. I like @dlang’s point of shortening the travel to lower the center of mass more. I’m agreeing with him that 3" of travel is a good amount for most needs.


#38

I am currently reading.

Quick question. Did you include the bricks in the CG calculation?


#39

Ran out of time tonight. I figured out a solution to choke point in the dust chute. I took your suggestions in the re-design. This is about where I’m at:

Center of Mass needs to be lower. I’m going to have to model the actual weights I want to use to get this dialed in more. I might raise the linkages further.

PS-20180425-2

I figured, though, why have a second face operation when you could just open the bottom up completely?

It’s close but I need to tweak it some more.


#40

Uhh, is now a good time to point out that I don’t yet have a working Maslow to do this? When I do, though, it’s happening.