[r-johnson]

Howdy all, long time lurker looking to finally build a machine.
expectations/ plans:

table size is about 10' x 2.5' looking for about 9' x 18" x 8" usable
High repeatably with an accuracy greater than .1 inches
Used solely in dense hardwood and laminate wood materials
Attached is the rough drawing of the base, steel welded/ bolted construction
Sqaure parts are 2x2" steel tube, angle iron is 3x3" (have a ton on hand) and rectangles are 4x1"
Plan on running the long axis on rack and pinion and linear rails.
Budget is around 5k

Now on to the questions:

1. I've heard conflicting things about building from the top down and the bottom up, is starting at the frame the right move?
1a. any advice on improving the frame/ making it more rigid?

2. I had planned to put the rack underneath the over hang but I'm wondering if this is the right move?

3. I haven't had any luck with finding rails and racks that are 9 ft long, does anyone make splice-able versions of both?

I'm sure this is the first of a thousand questions, I appreciate any advice!

[wizard]

Howdy all, long time lurker looking to finally build a machine.
expectations/ plans:

table size is about 10' x 2.5' looking for about 9' x 18" x 8" usable

This is a very long and narrow machine. Do you have a specific use in mind?

High repeatably with an accuracy greater than .1 inches

0.1 inches is pretty loose, I don't see you having a problem. Honestly though I'd strive for a bit more than that. Also how important is surface finish for you?

Used solely in dense hardwood and laminate wood materials
Attached is the rough drawing of the base, steel welded/ bolted construction
Sqaure parts are 2x2" steel tube, angle iron is 3x3" (have a ton on hand) and rectangles are 4x1"
Plan on running the long axis on rack and pinion and linear rails.
Budget is around 5k

Now on to the questions:

1. I've heard conflicting things about building from the top down and the bottom up, is starting at the frame the right move?
1a. any advice on improving the frame/ making it more rigid?

I would start on the frame first if I had the materials to do so.

As for making the frame more rigid there are things to consider:

1. For one I think I would avoid having the rails so high supported only by a few posts could be improved upon. Lowering the rails would allow cross members to contribute to supporting the top rail.

2. For the top member, the one you linear rails will mount to, I'd consider going to 3" square tubing. In this case not so much for strength or rigidity but to make sure you have plenty of room to mount you linear rails and rack. It should be noted that ""square"" tubing isn't exactly square so this could be a problem aligning every thing.

2. I had planned to put the rack underneath the over hang but I'm wondering if this is the right move?

Well protection from contamination is a good thing. You don't want to have chips getting into the rack. However a large overhand just leads to mechanical design issues. You should consider the shaft length of the gear box and whatever mounting bracket you come up with.

3. I haven't had any luck with finding rails and racks that are 9 ft long, does anyone make splice-able versions of both?

You can "splice" if you will but you should be able to find fairly long rails, I suggest going to the big manufactures and looking at the catalogs they have.

I'm sure this is the first of a thousand questions, I appreciate any advice!

Having plenty of angle iron is good. I would design around that angle iron supporting a square beam that is as long as the machine you want to build.

[ger21]

1) As long as your not designing as you go, then it doesn't really matter at all.

3) Racks are easy to splice. You just use a short piece of rack, clamped teeth to teeth, to align them.

Rails can be butt joined, but the seam needs to be nearly invisible. Manufacturers grind the ends for applications where multiple rails are to be joined.
Finding 9' rails is easy, unless you're trying to find cheap ones. I have a pair of 10' rails in a tube in my garage. Shipping them added 40% to the cost of the rails.

[r-johnson]

This is a very long and narrow machine. Do you have a specific use in mind?

0.1 inches is pretty loose, I don't see you having a problem. Honestly though I'd strive for a bit more than that. Also how important is surface finish for you?

I would start on the frame first if I had the materials to do so.

As for making the frame more rigid there are things to consider:

1. For one I think I would avoid having the rails so high supported only by a few posts could be improved upon. Lowering the rails would allow cross members to contribute to supporting the top rail.

2. For the top member, the one you linear rails will mount to, I'd consider going to 3" square tubing. In this case not so much for strength or rigidity but to make sure you have plenty of room to mount you linear rails and rack. It should be noted that ""square"" tubing isn't exactly square so this could be a problem aligning every thing.

Well protection from contamination is a good thing. You don't want to have chips getting into the rack. However a large overhand just leads to mechanical design issues. You should consider the shaft length of the gear box and whatever mounting bracket you come up with.

You can "splice" if you will but you should be able to find fairly long rails, I suggest going to the big manufactures and looking at the catalogs they have.


Having plenty of angle iron is good. I would design around that angle iron supporting a square beam that is as long as the machine you want to build.

Thanks for the reply!

The intention for the machine is making wooden propellers for airplanes.
They will still be finished by hand sanding but I would certainly like a tighter tolerance

1. The idea with having the rail so high was to have the spindle cutting in a well, both to contain chips and limit the gantry height. Would there be less flex in a taller gantry and flat table design?

2. The more I look at the rail mounting the more I hate it.

I know the mounting for the linear rails needs to be leveled and am exploring granite epoxy right now, how important is it for the rack to be dead flat? Trying to find off the shelf bracket/gear reduction,
but I think that means I'll be mounting to the side of the tube instead of underneath. I suppose it can still be mounted upside down.

can't seem to picture exactly what you mean by the last line

Thanks for the input!

1) As long as your not designing as you go, then it doesn't really matter at all.


3) Racks are easy to splice. You just use a short piece of rack, clamped teeth to teeth, to align them.


Rails can be butt joined, but the seam needs to be nearly invisible. Manufacturers grind the ends for applications where multiple rails are to be joined.
Finding 9' rails is easy, unless you're trying to find cheap ones. I have a pair of 10' rails in a tube in my garage. Shipping them added 40% to the cost of the rails.

Thanks!
Know of anywhere I can find a list of manufacturers for long rails and racks? I've been searching around and the best I can find it 8ft on both

[ger21]

All manufacturers make long rails. Where are you looking?

As for racks, just about everyone uses shorter racks and joins them together.

[r-johnson]

turns out I certainly wasn't looking hard enough, Thanks for the info on racks!

I'm also having trouble with sizing. How do you decide on profile rail width? I'm assuming it has to do with the weight of the gantry?
Trying to figure out how wide I need the rail mounting surface to be.

[ger21]

I'm also having trouble with sizing. How do you decide on profile rail width?

You look in the manufacturer's data sheets, which have all kinds of formulas for calculating rail requirements.

Or just use 20mm rails, which can typically carry several thousand pounds, and are more than adequate for any DIY router. 15mm will also work, but can be more difficult to work with due to their small size.

[wizard]

Thanks for the reply!

The intention for the machine is making wooden propellers for airplanes.

That explains it!

They will still be finished by hand sanding but I would certainly like a tighter tolerance

I would certainly strive for tighter tolerances. In the end the better you ability to finish profile to nice surfaces the less time you will spend hand sanding. Being a properly I would imagine there are balancing issues also.

The interesting thing here is that it might be viable to drive the gantry from one side. Your width makes this manageable but you would have to look into the mechanical design issues. Since you have pretty open specs for tolerance right now this could save you the expense of drives on each side if the X axis.

1. The idea with having the rail so high was to have the spindle cutting in a well, both to contain chips and limit the gantry height. Would there be less flex in a taller gantry and flat table design?

Obviously it depends upon the design but I prefer to make the lower frame as stiff as is reasonably possible. There are other things to consider though. For example these are airplane propellers and as such do you expect to do 4 axis machining of them. I've never even seen a propeller being machines so I'm not sure if the use of a fourth axis is common but it makes sense that it would be used.

2. The more I look at the rail mounting the more I hate it.

In a DIY machine the simpler the better. Which brings up the question of local machining support, in an ideal world your machine would be welded and then stress relieved. After which the mounting pads for the linear rails and racks would be machined. Obviously for a machine this size a well equipped shop is required, probably one with a planer mill.

I know you have pretty lose requirements for tolerance but do be aware of a couple of things, the more precise the linear motion components the more accurate the installation needs to be. This is especially an issue with shirt axises where you don't have the forgiveness of longer spans.

I know the mounting for the linear rails needs to be leveled and am exploring granite epoxy right now, how important is it for the rack to be dead flat? Trying to find off the shelf bracket/gear reduction,

Actually with a short and likely stiff gantry you will need for the linear motion components to be mounted fairly accurately especially with respect to flatness. Of course you can get different linear motion components with varying needs here but I would say your needs here are very high for dead flat surfaces. You can implement linear motion systems that can tolerate more misalignment but those are usually less stiff solutions.

Before I forget there is the consideration of squareness. Here I'm talking between the linear rails and the rack. You can't count on the tubing you buy being as square as is desirable for side mounting a rack. In other words square tubing isn't actually square in the sense that a machinist or a tool builder would desire. You need to take this into consideration when figuring out how your racks will be mounted. You do have options though, one would be to mount the rack on the same surface that the linear rails are mounted upon with the teeth pointed horizontally. This however requires a wider mounting surface for the components thus a larger tube size. There are a bunch of engineering decisions you will have to make here. Just remember there is no right solution just a whole bunch of trade offs. For your X axis though rack and pinion is probably the right choice.

but I think that means I'll be mounting to the side of the tube instead of underneath. I suppose it can still be mounted upside down.

Actually with Racks they are commonly mounted upside down. If not crap collects in the teeth which is not good.

can't seem to picture exactly what you mean by the last line

About the angle iron? If so what I meant is that if you have a lot of angle iron hanging around I'd design a machine that is mostly built from angle iron. This will take a bit of extra effort design wise as angle iron is awfully twisty but would save you a lot of money in iron. However my other point was that I'd still buy heavy square tubing fir mounting the X axis rails on.

On the flip side angle iron is less than ideal in places but you can work around its weaknesses.

Thanks for the input!

No problem, it is always nice to spend some one else's money!😳😳

One thing to note here is that we could potentially be over designing this machine. You suggested very loose tolerance requirements which is the opposite of what we often see here in this forum. Rather we see guys expecting far better than can be reasonably had on a home built machine. This is a good thing really, if we improve your expectations just a little bit I suspect that you will be very pleased with what comes off the machine.

Speaking of results it wouldn't be unrealistic to expect the machine to do at least some of the sanding for you. I don't see it easily doing everything but you may be surprised by how useful even a partially finished prop off the machine could be. Right now I'm imagining that to be really effective sanding would require four axis machining using simple pad attachments.

Which brings up another thing, tool changes? How many are required in normal machining of a prop? I'm really thinking that a tool changer will be needed.

As you can guess your expectation with respect to how close to finished the prop will be when it comes off the machine are important. Expectations are important in any machine build but in this case I really don't know what your process is.

Thanks!
Know of anywhere I can find a list of manufacturers for long rails and racks? I've been searching around and the best I can find it 8ft on both

Search for rack and pinion drives. A couple of companies should pop up right away. There are a number of turn key solutions out there including dual servo systems that are used in such a ways as to remove backlash. Some of these get to be expensive but I might suggest that you will benefit from servo (simple single servo) based systems over stepper based drives. This mainly due to the very long X axis and the likely hood that you will be running fairly fast feed rates and will be able to leverage very fast Rapids. In fact fast Rapids will likely be required other wise you will have a lot of lost production time.

[r-johnson]

the interesting thing here is that it might be viable to drive the gantry from one side. Your width makes this manageable but you would have to look into the mechanical design issues. Since you have pretty open specs for tolerance right now this could save you the expense of drives on each side if the X axis.

Was planning on dual drive steppers just to keep it simple. Not sure if I want to go through servo troubles on the first build. We'd also like to get this running in 5 months or so...

Obviously it depends upon the design but I prefer to make the lower frame as stiff as is reasonably possible. There are other things to consider though. For example these are airplane propellers and as such do you expect to do 4 axis machining of them. I've never even seen a propeller being machines so I'm not sure if the use of a fourth axis is common but it makes sense that it would be used.

redrew the frame, ditched the angle and its all welded 4x4 and 2x4. Seems a touch overkill but I like it better. Different manufactures use 3 or 4 axis, and while it would be handy I'm planning on keeping this one simple at first

In a DIY machine the simpler the better. Which brings up the question of local machining support, in an ideal world your machine would be welded and then stress relieved. After which the mounting pads for the linear rails and racks would be machined. Obviously for a machine this size a well equipped shop is required, probably one with a planer mill...
...Actually with a short and likely stiff gantry you will need for the linear motion components to be mounted fairly accurately especially with respect to flatness. Of course you can get different linear motion components with varying needs here but I would say your needs here are very high for dead flat surfaces. You can implement linear motion systems that can tolerate more misalignment but those are usually less stiff solutions.

Was planning on doing all the welding in house, I was under the impression mig welding didn't require normalizing? Short of heating joints with a torch its out of the budget unfortunatly...
I'm hoping an epoxy surface would be flat enough, it seems some people on this forum have had luck with it. Also, I moved the rack to the top as you described its just not depicted with teeth.

No problem, it is always nice to spend some one else's money!😳😳

Oh I know, thats part of my day job!

Right now I'm imagining that to be really effective sanding would require four axis machining using simple pad attachments.

I had no idea this was even a thing!

Which brings up another thing, tool changes? How many are required in normal machining of a prop? I'm really thinking that a tool changer will be needed.

As of right now it only looks like two tools, this could change as I research more tooling


Thanks a ton for the in depth responses!