5 axis Gantry style Milling Machine prototype

[mikechandley]

Hello my Name is Mike Chandley.

I have been reading many build threads and this will be my first design.
I know its a challenge for a beginner but I have a pretty good mechanical background and have designed several other mechanical things in the past.

True 5 axis and D.I.Y. doesn't seem to get a lot of positive feedback on this forum. (I do understand why but I accept the learning challenge.)

My preferred material for this design will be Aluminum and yes that means the dreaded Extrusions lol.
My feelings are with the proper design aluminum will get get the job done. Look at airplanes.
I'm trying to keep the weight down, as the design progresses you will understand why.

The working area of this machine is 21"x 31" z travel approx. 6" My goal here is to keep as small of a footprint as possible.

My (con-fusion) Fusion 360 experience is 26 days at this point so bear with me lol.

I do not have the total machined completely drew up at this point...too many questions to try to finalize this design.

To save confusion of all the components at once I will give preliminary drawings of my thinking and my questions.

The components for the first picture are the spindle motor witch is a 12,000 rpm 2.2 KW motor, the Spindle holder, side plates and side plate braces, Harmonic drive FHA_CH 100-17.

I chose 6061 1" thick milled to .950 for the plates.
1st question is which Type of plate alloy is best for this application.

For the spindle holder what alloy? If different? as it will basically be machined from a block.
Spindle holder dimensions are 8.5" tall" 8" Long X 5.349" Deep
The end of the spindle is a 6"diameter Diamond Cutting blade

The side plates are 10" wide at top narrowing to 5" at bottom for Harmonic Drive they are 12.052 in length witch includes the .125 recess into the top plate.

The top plate is a 12"Circle .950 thickness

the side Braces are .950 thick 2.125" at top Narrowed to 1.125 at the bottom to fit in recess.

The material I will be cutting is Granite, I spent 15 years of my life cutting stone by hand in my Granite businesses and I can tell you the approximate load at the blade would be
350 in. oz. of torque to push through the 1.25 thick stone.

So the expected load on this machine is 35 foot lbs. at the tool end. Hopefully this will answer a lot of the questions about what is needed for the rest of the design.

This will be a long winded thread so... Thanks to all who's input is so much appreciated.

Lets get started.

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[awerby]

If I was designing a machine for carving granite, I'd want to protect everything with bellows, since the dust and slurry is abrasive and gets into everything that slides, ruining it quickly.

It seems like that spindle is somewhat light-duty for granite; I'd want something beefier, especially if I was using it to power a saw blade. Or is there a separate saw arbor and milling spindle?

Granite-cutting machines I've seen have all been big and heavy. Is there some special reason you're making yours small and light?

Fusion 360 doesn't support 4th, 5th or 6th axes. Are you planning to migrate to different software when you add the extra axes?

[mikechandley]

If I was designing a machine for carving granite, I'd want to protect everything with bellows, since the dust and slurry is abrasive and gets into everything that slides, ruining it quickly.

It seems like that spindle is somewhat light-duty for granite; I'd want something beefier, especially if I was using it to power a saw blade. Or is there a separate saw arbor and milling spindle?

Granite-cutting machines I've seen have all been big and heavy. Is there some special reason you're making yours small and light?



Fusion 360 doesn't support 4th, 5th or 6th axes. Are you planning to migrate to different software when you add the extra axes?

1. It will all be protected with a guard on blade and seals and covers. The Fha-17-ch Harmonic drive is a wash down design.

2 I've cut 100s of 1000s of linear feet of granite with a Makita 9565 12 amp side grinder with a 6"blade at 10,000 rpm this spindle has over twice the hp.
also there is no room for a larger spindle than 85 mm 3.346 diam. As a matter of fact the spindle body will protrude through the bottom of the spindle holder'
Ive already designed for that. 3.346 divided by 2 equals 1.673 inches subtract by 1/2 blade diameter of 3 inches leaves 1.327 working depth.
Getting a blade made for whats needed is no problem. There is a reason i'm leaning towards the 6" diameter.

3 Im using Fusion 360 for the design...if it will not drive the machine I will purchase whats needed. I think it supports 5 axis on cam side?? not sure.

4 Look at the tool cutting force foot lbs for the design...forget the word granite that scares people to death lol.

Thanks

[NIC 77]

I can't really tell from your explanation what you are going to do for bearings. For what you have drawn, you'd need to have bearings on both sides and then drive that with the harmonic drive. Also a bearing on top.

You could use two large harmonic drives with flange output, that would be so much easier to make IMO then what you have drawn. Also, harmonic drive is a brand name, with their proprietary way of doing things, but there are other planetary manufacturers, such as alpha wittenstein that have planetary models with less than one arc minute of backlash that you might consider also.

You mention using aluminum extrusions. I assume you're talking about T Slot extrusions. OK, I don't see this as being a good choice for a stone cutting machine. There, I said it.

Oh, I see you're also talking about aluminum plate, OK, I have no problem with this. 6061 T6 is good. You are building for stiffness, and this has almost the same modulus of elasticity as the more expensive alloys. Ultimate strength isn't so important. So you're going to seat some bearings in this aluminum plate?

You didn't mention what your budget is on this.

I have put some thought into what I would do if making a 5 axis machine due to some other threads in this forum.

I have decided that I would scour North America looking for a good used robot arm and turn table and voila, machine is built.

Like this



Just an idea. But if you can find a good used robot arm for a good price.......well, that's my 2 cents. Please continue posting with what you decide to do, I'm interested to see what direction you take and how this works out.

[mikechandley]

I can't really tell from your explanation what you are going to do for bearings. For what you have drawn, you'd need to have bearings on both sides and then drive that with the harmonic drive. Also a bearing on top.

You could use two large harmonic drives with flange output, that would be so much easier to make IMO then what you have drawn. Also, harmonic drive is a brand name, with their proprietary way of doing things, but there are other planetary manufacturers, such as alpha wittenstein that have planetary models with less than one arc minute of backlash that you might consider also.

You mention using aluminum extrusions. I assume you're talking about T Slot extrusions. OK, I don't see this as being a good choice for a stone cutting machine. There, I said it.

Oh, I see you're also talking about aluminum plate, OK, I have no problem with this. 6061 T6 is good. You are building for stiffness, and this has almost the same modulus of elasticity as the more expensive alloys. Ultimate strength isn't so important. So you're going to seat some bearings in this aluminum plate?

You didn't mention what your budget is on this.

I have put some thought into what I would do if making a 5 axis machine due to some other threads in this forum.

I have decided that I would scour North America looking for a good used robot arm and turn table and voila, machine is built.

Like this



Just an idea. But if you can find a good used robot arm for a good price.......well, that's my 2 cents. Please continue posting with what you decide to do, I'm interested to see what direction you take and how this works out.

1 This is a flanged style Harmonic Drive from Harmonic Drive.net
If I go with this style unit yes there will be a bearing assembly on the other side.
I do like looking at other options as this particular model is not readily available...6 months from order! And it is not cheap lol close 3k
I have also drawn this up with a belt drive using tapered roller bearings 2 per side see attached drawing.
not sure if this a option but would defiantly be cheaper.

2 Yes there will be a bearing assembly in the top for forth axis rotation.
I would rather not jump that far forward yet as to save this thread from getting confusing.
One component area at a time is my goal lol.


My preliminary thinking is in the 20k budget range.

No challenge in buying a robot that would be to easy.

Just remember this is a prototype that I hope to perfect for resale in some way shape or form.
Might be a bad idea just posting this.

[mikechandley]

pic

[mikechandley]

another

[mikechandley]

last one of the Harmonc drive flanged style mount

[ger21]

What's the intended purpose of this machine? It can't be just for cutting granite, at such a small size?


You mention 350 oz-in of torque, and then say 35 ft-lbs? 35 ft lbs is about 6700 oz-in.

That drive has a continuous torque rating of 23Nm, which is about half of the 35 ft lbs. So if you need a continuous 35 ft lbs, it's probably not going to work.

Did you choose that spindle because it was cheap? My guess is that the rpm is much higher than you need for stone, and would shorten blade life.

Looking at HSD's website, their stone spindles are 12,000 rpm, but their saw aggregates are geared down to 3500 rpm.

[mikechandley]

What's the intended purpose of this machine? It can't be just for cutting granite, at such a small size?


You mention 350 oz-in of torque, and then say 35 ft-lbs? 35 ft lbs is about 6700 oz-in.

That drive has a continuous torque rating of 23Nm, which is about half of the 35 ft lbs. So if you need a continuous 35 ft lbs, it's probably not going to work.

Did you choose that spindle because it was cheap? My guess is that the rpm is much higher than you need for stone, and would shorten blade life.

Looking at HSD's website, their stone spindles are 12,000 rpm, but their saw aggregates are geared down to 3500 rpm.

1 Yes just cutting granite. Sink holes

2 Im no engineer but I can tell you if you pull 35 lbs of force with your hand against a custom made tool cutting into the stone you will be taking a very deep cut of .250 of material at a time. Think of it as pulling a 1/2 end mill into the side of a solid aluminum 1.25 thick block at full depth of 1.25 inches not step cutting.
35 lbs is truly overkill for the load this machine will be under. The amount of material to removed to get to finished size can be adjusted by depth of cut. The spinning blade{s} and the spindle motor do the work. Truly 15-20 lbs of force will get it done quickly. I am trying to over think the stresses and be safe with my calculations.

Large Granite cnc machines cut sink cutouts by using a .500 diamond coated finger bit @ 5000 rpm full depth after coring out a hole with a faucet bit. some machines still step cut the cutouts. These are 20 hp spindles cutting at about 5 inches per min at full depth. so about 20-40 min per sink hole of machining time on a 250k machine. Thats just to drop the cutout still has to be polished'
Large granite diamond blades turn at 3500 rpm for 14 in diameter 3/16 wide blade big saws usually 20 to 30 hp to turn that animal.
6 inch diamond blades are turned at 8500-10,000 rpm.

There is no faster way to cut granite than with a spinning diamond blade.

It takes me 5 minutes by hand to put a sink cutout on the ground with a 6" right angle 12 amp model 9565 Makita grinder and a 6 inch blade. Don't concern yourself with the corners I have that all figured out.
Now I'm designing this machine to do what I know can be done by hand.
Thats all I'm going to say about the purpose of this machine.

2 So if im pulling 20 lbs of force against a tool is that ft lbs?

35lbs of force against the Makita will overload the grinder to a very low rpm. I will call it 18lbs of pulling force average if that is 18 foot lbs then its 3445.714 ounce inches.

3 The spindle was not picked because of price witch is around $800 It was chosen because its a metal working designed 2.2 kw water cooled spindle with a 5000-12000 rpm range.
This should be over double the power of the makita 9565.
Plus once again I'm limited to a 85 mm dia. spindle because of the blade diameter.

Thanks
I hope this makes more sense.

[mikechandley]

I thought about the questions earlier about the Harmonic drive. This unit has a built in Brushless pancake servo motor with a flange mount. nothing more is needed to turn the spindle mount other than a bearing to support the load to the other side plate.

[ger21]

You need to make angled (beveled?) cuts for sink holes? What happens in the corners? What I'm getting at, is do you need 5 axis? Or just 4?

2 So if im pulling 20 lbs of force against a tool is that ft lbs?

No, it's not a straight conversion from force to torque.
Divide the force by 1/(distance from pivot point to where the force is applied.)

So, if your blade is 6" from the center of the harmonic drive, it's 20lbs / (1/0.5ft), or 10 ft-lbs.


You might want to consider looking at a higher end spindle, designed for stone. It may cost 3x-5x more, but I would expect that chinese spindle to be the weak link when the design is complete.

[ger21]

I thought about the questions earlier about the Harmonic drive. This unit has a built in Brushless pancake servo motor with a flange mount. nothing more is needed to turn the spindle mount other than a bearing to support the load to the other side plate.

Yeah, I looked it up on their site.
Does the $3K include the drive? If not, I'd expect the drive to be another $1k.

[mikechandley]

You need to make angled (beveled?) cuts for sink holes? What happens in the corners? What I'm getting at, is do you need 5 axis? Or just 4?




No, it's not a straight conversion from force to torque.
Divide the force by 1/(distance from pivot point to where the force is applied.)

So, if your blade is 6" from the center of the harmonic drive, it's 20lbs / (1/0.5ft), or 10 ft-lbs.


You might want to consider looking at a higher end spindle, designed for stone. It may cost 3x-5x more, but I would expect that chinese spindle to be the weak link when the design is complete.

1 yes I need the 5th axis for two reasons..
1 for cutting ovals we use a contour diamond blade as you progressively step cut the oval shape, the 5th axis will help keep the blade in the center of the started cut you will still be swarf cutting but it will minimize the amount of material removed.

2 After dropping the kitchen sinks with a straight blade into the corners I will change tool to a vertical stack of 3" blades to size the hole, then a 2" diameter diamond tool will clean up the blade marks preparing for the polishing.

If i can get a custom spindle made for what i need Ill gladly do it..I have a estimated budget of 20k on this machine so if its over or under it is what it is.

After watching other build threads on steel frames its not that hard and I have a machinist friend that will help in all the machining process and steel is not that difficult at this size.
the Z axis will probably still be built with aluminum parts and steel combined.

i enclosed a pic of when the macine is used as a milling end and a pic of how I plan to mount the spindle without fully encasing it. This will allow for full depth cutting with the 6 inch blade.

[mikechandley]

Yeah, I looked it up on their site.
Does the $3K include the drive? If not, I'd expect the drive to be another $1k.

my quote for that drive was $2500 thats not the wash down version lol i figure another $500 plus the drive.
Look at FHA-17-CH -100 thats a wash down 100 to 1 reduction unit.

If I can do it with a servo motor and a belt drive it will save a ton of money...look at the next picture i post.

[mikechandley]

This was my first thought using four tapered bearings two per side. 5/8 diameter shaft

[mikechandley]

better pic

[ger21]

I would not do it like that.
I'd use a gearbox like an SHF-17-100-2SH, and put a pulley on the gearbox. I'd be worried about belt flex doing it the way you are showing.

[mikechandley]

Ill check it out Thanks

[mikechandley]

Ill post some pics of the Y axis gantry.
this was the original design before I realized it can be cut down from 48 inches in pic to 38 inches now with the new spindle holder design.

this is 40-40x80 8020 profile with 4 hiwin 20 mm rails and 8 bearings. end plates are .950 aluminum side braces are .480 aluminum. .980 base bearing blocks.
this is 14.294x14.294
the Z axis will will be in the center.
every joint is recessed to keep square