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View Full Version : Help planning a small(?) router for aluminium please



suicidal_orange
07-02-2018, 03:54 PM
I'm in the learning/pre-planning stage and am trying to get my head round what to buy for my first machine.

I know everything will make more sense to me once I've got my hands on a machine (or better yet the parts to build one) because that's how my mind works. But I'm hesitant to buy something so small or cheap it's useless or to invest much in a decent small build which would eat into the budget for a potential 'proper' build later when I think I'm starting to understand how all the bits fit together. All things considered the best option seems to be trying to plan the build I really want blind.

Based on the idea you should always go bigger than you think you need I'm looking at a working area of 400x200x200mm and will be using the machining friendly aluminium.

I have fallen at the first hurdle though as I'm not sure whether to go for a 200mm moving gantry or a 400mm fixed gantry with a moving bed. When reading moving bed is only recommended for 'small' machines but that's relative - compared to the door size monsters some people make I would say this classifies as small, but 400mm is more than half a door so maybe it's not so small?

I'm thinking moving bed would be easier/cheaper but would like to give someone with experience the chance to say that it's not much harder (or maybe easier as it's so small?) to create a rigid 200mm moving gantry than a 400mm static one, not least because this would make the machine significantly smaller.

Thanks in advance for any thoughts.

Clive S
07-02-2018, 04:10 PM
I'm in the learning/pre-planning stage and am trying to get my head round what to buy for my first machine.

First of all its best to keep all your posts in one place as the thread will be easier to follow. Wal this is his blog https://wrbl.tumblr.com/mill-build has built a small mill with a fixed gantry.

Do you have a budget in mind? What ever you do don't buy any kits as they are never matched and ask plenty of questions.

suicidal_orange
07-02-2018, 04:36 PM
Thanks Clive, I kept the title vague and was just going to update the first post with new questions rather than spamming lots of threads then when/if it happens I'd start a build log.

I don't want to be wasting money on materials and tooling because I skimped on the build so was thinking I would learn and plan what I should get to meet these specifications but keep saying I want to keep it cheap so people don't suggest premium options (unless they warrant the extra spend over a capable alternative), then when I have a plan I'll start looking at prices. If it comes out too much so be it, I'll have learned lots and will be able to consider a smaller, less future proof, build. I may win the lottery by then and not care about the price!

The linked machine looks nice but looks like a moving table on X and Y? I was planning on having the spindle move on the gantry, though I guess it's partly the same... Not seeing any text yet so will check back later.

Do I take the linking to a fixed gantry to be you saying that is the cheapest option for this size machine?

JAZZCNC
08-02-2018, 09:51 PM
Hi,

Fixed or moving gantry the cost will be very similar. Swings and roundabouts really. What you save on one style you'll ie: shorter rails/ballscrews you'll lose on other ie: more frame material etc. So suggets you forget costs and choose based on whats best for your needs.

So would be better if told us what want to do with machine.

Now biggest mistake people make is trying to build on the cheap.and buying/designing on the fly with result 99% of the time ends up costing them 1/2 much again because they buy cheap components then realize not up to the job or design changes so useless.

The best approach to building a machine that will fit your needs exactly and happen in a stress-free manner is to research and design the machine to a decent level of accuracy before doing or buying anything.
Then when you have design nailed down it will lead you to material and component sizes etc so can get accurate costings.

Building a great cost effective machine isn't difficult but it's very easy to go about it wrong and starting off with a mindset of Cheapest is not a good approach IME.

suicidal_orange
09-02-2018, 12:28 AM
Thanks JAZZ

As I said I'm planning to a spec greater than I need and will not buy anything until the plan is complete, cost is the second consideration (if the plan to do what I want is too expensive it just won't happen)

It's hard to come up with a design when everything I read seems to talk in 'small' and 'large' machines with no indication what this means - if it said a rail less than 300mm is small, more than 600mm is large that would be meaningful, the words alone are not...

My main planned use is 60% keyboard cases which are basically hollowed out blocks of around 290x110x30mm - proper aluminium milling. The Z axis is big to allow for drilling holes in the back and so I can add a 4th axis at a later date.

Would be good to know what of the above leads you to suggest fixed or moving gantry please, I want to learn.

JAZZCNC
09-02-2018, 05:35 PM
It's hard to come up with a design when everything I read seems to talk in 'small' and 'large' machines with no indication what this means - if it said a rail less than 300mm is small, more than 600mm is large that would be meaningful, the words alone are not...

Ok get what your saying but this is why we say research and then bit more research because without doing it you'll always be unsure of exactly whats required for your particular needs.

But to help you lets start by clearing up "Small" "Large".

Simple answer is there's No such thing really because one man's small is another man's large or vise versa.?
Ie some would consider travels of 300x300 small but if your making say wedding rings then this is massive.

So really your better just choosing the cutting area you think you'll need then design and spec from that.

Now to help you in terms of what's best Fixed or moving gantry then it basically boils down to this.

Fixed gantry is generally stronger because of the more rigid frame structure. However, this design requires more area for the same travels as Moving gantry design would require. So this design tends to suit smaller machines better because for large machine would take more space and require longer rails, ball screws etc than would moving gantry.
If wanting large cutting area ie: Router then moving gantry design is often a better option as it's more cost effective and space saving.

So from what you say my suggestion is Fixed gantry. By this I mean Moving table for Y axis and X axis moving across the Fixed gantry unlike Wals design which basicly works on same principle as milling machine with X & Y on moving saddle type arrangement.

Regards Spec then will be guided by budget mostly but it's here where cutting corners will bite you later down the line.

Can tell from lots experience if your wanting to seriously cut aluminium then you really will need profiled linear rails like Hi-win if you want best finish.
In terms of rail sizes then again depends on factors like loadings etc. But to keep things simple I can tell you for fixed gantry machine around say 400x400 cutting area then 15mm rails will easily handle any loads your likely to place on them.
However if your wanting little more ridged machine then 20mm will be better option and not lot of difference in price terms. This would be my choice.
If wanting really ridged machine then 25mm but in terms of loadings these will be massively OTT.

Now ballscrews will be next on list. This is an area where can often confuse and catch people out.
With Ballscrews you have 3 main things to consider or spec up.! Class, Pitch & Diameter. Each breaks down into sub options or classifications.
# Class = The precision and efficeincy of movement.
#Pitch = The amount of distance traveled for one revolution.
#Diameter = Well no brainer this one.!!

Class can be broken down into 4 classes. C1 C3 C5 C7. The highest class is C1 which means it will higher precision and higher efficiency than next class down. It will also have hefty price increase to match.
Also there are 2 grades of screw, ground or Rolled. Ground being more accurate than rolled. Like wise ground screws come at premium.

Now for Hobby level machines then Rolled C7 is mostly used because cost's vs spec. If want that bit better then C5 but the price increases accordingly and when gets past C5 the prices become eye watering. Also above C5 you move into ground screws territory.

Pitch is next consideration. Choosing pitch is combination of resolution required vs Feeds required. Lower pitch will give higher resolution but require more RPM achieve same feed rate as higher pitch screw.
ie: 5mm pitch with 1000 rpm motor will allow 5000mm/min but 10mm pitch will allow double this because travels double the distance for one revolution.
There are other factors come into play when choosing pitch, like how fast screw can spin before whipping but won't get into that now because will only confuse and doesn't really come into play on small machine.

Typical pitch for machine like what you require is 5mm. This will give good resolution while allowing decent feed rates which will suit variety of softer materials other than aluminium.

Diameter is obviously what it says but the importance comes into play depending on screw length and torque loadings etc. However for your needs forget torque/loadings because even smallest diameter will cover your needs.
The diameter to some degree will determine what pitches are available. Smaller diameter screws tend to be lower pitch and used on shorter machines because they whip and fibrate easier over long lengths.
Whip is factor of RPM, Diameter and Length.

Small pitch would be <=2.5mm and diameter <=12mm. Medium pitch 3-10mm D12-20mm. Higher pitch 25-50mm D25-50mm+

For your needs then C7 D16mm with pitch 5mm will be perfect.
This spec when coupled with stepper motor that will provide aprox 800-1200rpm depending on other factors like voltage which comes little further down the line when choosing electronics etc, will give feeds in the region of 4000-6000mm/min or more and resolution in realistic worse case scenerio of 0.025mm.
In reality you'll get higher than this because of other factors like micro stepping but that's worse case for stepper with No micro stepping applied which you would apply for other reasons, which again will be explained further down the road.!! . . . . Building CNC machine is like eating Elephant.? Small bites digested slowly.!

Ball screws need to be ridgedly mounted to machine and this is often done using Special bearing blocks known as BK/BF bearing blocks.
There are other types but these are most common.
Typical ballscrew will have Fixed end which holds the screw and stops any axial movement this end would use BK block. The other end is held with BF block which floats to allow for thermal expansion.

So to recap and get you going in right direction.

Fixed gantry if lower travels than say 500mm. Suggest 400x400 for your needs.
20mm Profiled linear rails for best balance of strength/cost easy of building.
Ballscrew C7 D16mm x 5mm pitch.
BK/BF end bearings depending on design.

I would also suggest Steel contruction of main frame for best balance of cost to strength.

Hope this helps. Start build thread even with out having design nailed down and ask all questions there it's easier to keep track of replys.

suicidal_orange
09-02-2018, 07:24 PM
Thanks again JAZZ, that went slightly beyond the question asked! I do have one final question before I attempt a rough plan and start a build thread please, should be an easy one.

A 400x400 cutting area will take up nearly double the space compared to my planned 400x200 which is already bigger than I can think of a use for - why do you recommend this size? I'll need a bigger table!

JAZZCNC
10-02-2018, 01:36 PM
Thanks again JAZZ, that went slightly beyond the question asked!

Well suppose yes but same time no not really because only gave you the basic run down and you'll need to know this info to come up with good design/machine which suits your needs.


A 400x400 cutting area will take up nearly double the space compared to my planned 400x200 which is already bigger than I can think of a use for - why do you recommend this size? I'll need a bigger table!

Well, really it was just to give an idea of a small machine with a reasonable cutting area that gave little room to expand from what you think you need.!!

Like I said size is relevant to the user or purpose. However, I can tell you as will others with 99.9% certainty that when getting into CNC you'll want to tackle larger jobs and soon even 400x400 won't be enough.!

Clive S
10-02-2018, 01:47 PM
A 400x400 cutting area will take up nearly double the space compared to my planned 400x200 which is already bigger than I can think of a use for - why do you recommend this size? I'll need a bigger table!Don't forget you will need hold down clamps on the table as well.

suicidal_orange
10-02-2018, 10:36 PM
Don't forget you will need hold down clamps on the table as well.

This is why half of me still thinks I should buy a near useless <150 Chinese 1610 or similar - I can't forget about clamps as I'd never thought of them! Just had a look and seems you're supposed to make them out of wood so can't really see how much bed I'll lose. Very random...

Thanks for pointing out what should have been obvious!


Like I said size is relevant to the user or purpose. However, I can tell you as will others with 99.9% certainty that when getting into CNC you'll want to tackle larger jobs and soon even 400x400 won't be enough.!

I've just measured and I have 405x910mm of table so 400x400 travel isn't going to fit. That leaves me with two options: 400mm (or bigger? Don't think there's any point...) fixed gantry with 200mm travel bed using a rack and pinion (no room for a motor on the already small 200mm axis or a 300/350mm fixed gantry (depending how thick the sides are) with 450mm travel bed, which could use ballscrews.

Apart from the drive everything will be the same apart from lengths so I can plan most of it and decide on the size later (you and everything I've read say you always want bigger so if budget allows why not)


I'm now wondering how much weight the table can take though, and whether it needs to be level and/or flat. I was thinking 4 feet in the corners would be sufficient as the frame will be rigid by design but hadn't considered weight at all. Any suggestions for testing a table without destroying it?!

I still have plenty of reading to do - thanks again for the solid intro.