[merlin777]

So, a newbie here looking to tap into the huge depth of cnc experience here.

I used to enjoy woodworking decades ago but life got in the way and I couldnt keep it up. More recently I became ill and ended up in a wheelchair with more time on my hands so I decided to set up my workshop again only this time in miniature, using dremel-type tools and making small ornamental items like clocks and boxes.

There's one thing I want to achieve in particular - decorative spiral cutting.

Maximun 2" x 8" hardwood stock. down to min 1/2" x 4" stock
Both right hand and left hand twists
various pitches from a gentle thread to 3 or 4 start twists
hollow spirals
and one i'm REALLY exited about which is varying the pitch during the twist!

I'm a low-income hobbyist and my poor mobility and wheelchair exclude anything large or expensive. I have good diy skills but not fine engineering skills e.g. I couldn't refurb a lathe but I could build a cnc kit.

I've looked at lathes, mills and routers.

What I think so far is that wood lathes would be no good for accuracy on my small pieces. They can't cut threads. Metalworking lathes are more appropriate but it's tricky changing the gear wheels to give me the range of pitches I want (including RH/LH threads and varying pitch) so cnc would have to be required.So, if I'm going cnc then I might as well look at milling and routing because I will be able to do so much more - engraving, intarsia and so on.

So - mill or router? From what I've read so far, mills are more accurate than routers but routers can machine a larger area. I nearly committed to a proxxon MF70 with cnc kit and I was going to add a rotary table 4th axis - then I found out I could only do a panel of around 3 x 6 inches. Not a lot for the money.

Mill or router, scratch-build or convert? (Bearing in mind my modest skills and budget) Although the objective is the spiral spindles, i'm in this to learn and have fun so the journey is as important as the goal.

I'd love to hear your thoughts and recommendations!

[wizard]

If your primary material is various types of wood, a low end mill will not do. That is due to the slow spindle. Oh by low end im talking hobby sized desktop mills. There are ways around the slow speed spindle but i will ignore those for now.

In any event lets say that a router sounds like the right approach here. You need one large enough to accomodate a suitable fourth axis. A machine with an 18" square working area should work well with a variety of fourth axis solutions with room to spare. You could go even smaller depending upon the fourth axis and its dead center. In the end you are better off with a machine that is larger than initially required simply due to capabilities you can grow into. On the flip side too big wastes space and routers can waste lots of space.

You mentioned Dremels but we need to warn you that they dont work well at all for spindles. In fact in a CNC they can fail very fast. Your best bet is a Chinese spindle. Other wise you can choose from a number of small routers for such a machine.

I dont know the specifics of your disability but the assembly of a kit may be a problem without help. Going even further DIY, may be even more difficult. There are commercial machines in the suitable size range but most of these are not cheap.

Speaking of commercial machines there are Chinese machines avalable for relatvely low cost. These are often considered to be kits even if sold as working machines. However on most of them the basic structure isnt bad.

If you have more questions please post again in this thread. In any event it is a good idea to get a handle on your expectations, available space and local support. Local support means suppliers, machine shops and so forth that could help with subassembly fabrication. If your current shop is very limited you need to either buy kits or have custom machining done.

[merlin777]

Thanks, Wizard.

I hear what you say about underestimating the size you'll need - as I discovered with the MF70. My disablity will limit me in terms of heavy or prolonged work so a modest tabletop machine would be fine as long as I can break the work up.

A few quickies, if I may?

By a chinese spindle do you mean a router motor like this? https://www.aliexpress.com/item/BEST...ceBeautifyAB=0

What are good strategies for a 4th, rotational axis? I was considering a cnc-driven vertically mounted rotary table but I'm open to suggestions.It would work with my custom design (if I can draw it I'll post it!) which is more lathe-like but on a flat bed/gantry style I'm concerned it'll be too heavy.

Lastly, I'd happily consider a chinese quasi-kit but I took a look and the choice of machines and prices is bewildering. Does CNCZONE have an area where they are discussed?

Cheers, wizard.

[ger21]

By a chinese spindle do you mean a router motor like this? https://www.aliexpress.com/item/BEST...ceBeautifyAB=0

No, those are lightweight junk.

Something like this.
https://www.ebay.com/itm/800W-220V-E...EAAOSw2s1UtyXj

What you want is a desktop router with a rotary 4th axis.
https://www.ebay.com/itm/1500W-VFD-4...sAAOSwwZtaXWFa
These machines are the cheapest way to go, but in some cases require modifications and electronics upgrades.

[merlin777]

Thanks, Wizard. I'm off to do some research. I dont think I'll out grow a 3040 very quickly and that'll keep the price down. Will a gantry router still have the potential for fine quality work (assuming quality components and set up etc)?

This was my first stab at a lathe-style helical spindle cutter (attached). Single-purpose but very cheap.

[ger21]

Those 8mm guide rails will flex like a wet noodle. Literally. Even if they were 16mm, they'd have to much flex. The general rule, is avoid unsupported rails at all cost.

[merlin777]

thanks for the warning - could you give me an example of supported rails?

[wizard]

Thanks, Wizard. I'm off to do some research. I dont think I'll out grow a 3040 very quickly and that'll keep the price down.

You are in a position where buying a smaller machine can lead to a stiffer machine assuming that the machine was well designed in the first place. The only real problem is that a machine that is too small for the 4th axis you choose will be useless. This is why understanding the space needed by your 4th axis is so important.

Will a gantry router still have the potential for fine quality work (assuming quality components and set up etc)?

That all depends upon what you are comparing it to. In general a decently solid gantry type router will do well in most woods.

This was my first stab at a lathe-style helical spindle cutter (attached). Single-purpose but very cheap.

A single purpose machine can have some advantages but it is hard to see those advantages at a low price. Consider your design, which i would not build, how will you machine the various components, Even if you start with an old wood lathe you will still have lots of machining to do. Custome machining for a one off build gets expensive fast.

In any event lets say money isnt an issue for this or that you have a buddy lined up to do the machining. You then have to consider if the design is workable. In my estimation it isnt as it ignores considerations for stiffness and spindle size.

Stiffness or the lack of comes from the skinny, unsupportted round rails. Considering the short strokes you might be able to get by with much larger diameter round rails but in general unsupportted round rails are bad for machining operations. Ideally what you would want is profile rails mounted to a stiff integrated structure, that keeps the rails parallel to the mechanical features that align your headstock and tail stock. For a small machine like this you can machine all of these features in one setup on a small mill like a Bridgeport. Building a suitable headstock and tail stock isnt that hard but it does involve more custom machining. In any even back to the slide that will carry your spindle, you really need to be carefull about component stack up and the final spindle centerline height. You pretty much have to design your machine around this stack height as you need the two spindke centerlines at the same height. In most cases you do anyways but one big advantage of a router is the ability to move the cutter off the centerline. There are several reasons why you might need to move the cutter off the centerline but the most obvious is to machine flat spots on a spindle. In any event id you decide that you need spindle movement up and down that needs to be factored into your slide mechanism that holds the router spindle. In any event as you add up these features your lathe spindle has to be higher and higher or you end up with a more complex mechanical structure. Of course more expensive but physically small spindles can help here or maybe even a DIY spindle.

You could save some time and money borrowing components from a small lathe systems like Sherline or Taig sells. Consider what they have carefully because the physical size might not be suitable for your needs. However if the components do work you save a lot of time and effort in machine design and build. Essentially you would end up bolting a set of ways to a tooling plate which has your CNC slide attached. My big concern here is that you would have enough stiffness in those components.

Another approach would be to take a metal working lathe such as a 7x14 and mount a router spindle on the cross slide. This involves a lot of machine rework to get to a CNC solution. Frankly these sorts of lathe conversions leave a lot to be desired. By the way most of these solutions really need to be two axis for router spindle positioning with the lathe being a third CNC axis. This is a lot of machine building that is taken care of on a prebuilt router.

In any event before investing in anything here i would highly suggest reading as much as you can on the subject of DIY CNC. Im left with the impression that you need to expand your fact based knowledge before commiting to a machine design. At this point i would suggest a small router over a custom machine build but that is based on a limited understanding of your needs. Once you expose your self to all the different possible approaches to this, you should be able to determine what best fits your need.

[wizard]

thanks for the warning - could you give me an example of supported rails?

Search for fully supported round rails for examples of supported round rails.

Ger might have had profile rails on his mind such as those from THK or HiWin. These are often a much better choice for machine tool construction. I say often because sometimes it is simply more economical to use round rails where profile rails aren't needed. Also supported round rails can often provide for a tunnel to run the ball screw through.

There are many trade offs to be made with the various mechanical components that you can buikd a machine out of.

[merlin777]

Much to consider there, thanks, Wizard.

I'm a planning-type person rather than a 'just wade in and do it' type person so I'm on a journey of education and discovery before I touch a piece of hardware. I learn something with every forum reply I get from you guys, so thanks for that.

I'm not in a position to do - or get done - machining and that might ultimately mean just saving up to get a decent 4 axis hobby level router but I'd like to check out other avenues first. It might just be that its worth a few quid to get hands-on of some components just so I can understand how everything works and where the problems are. The devil is usually in the detail.

The early design I have uses all readily-available components and draws on successful projects people have already documented. For instance, you can source mounting plates to attach a nema 17 or 23 to the milling table .I've chosen. I'll definitely be looking for a stiffer support structure now. The tool height was an issue originally but I was going the put a manual vertical adjustment under the tool for those rare occasions I'll need anything different to exact centre height. I went through the helical spindle turning process from square stock to finished item and at the moment I can't see a need for an offset. I considered side mounting the tool on the cross slide to keep height down. I tired to design-in short and tight rather than long and loose as good practice.

My spindle was going to be a vertically mounted rotary table with compatible 4 jaw chuck and a stepper motor mounting kit. Solid but heavy. I'm still looking for alternatives because it seems a bit overkill.

I share your view of the lathe conversion route.The amount of machining is a no-no for me for a start. It was my first approach and converting all 3 axes to CNC unless there's a kit would be too much of a hill to climb.

I really appreciate the benefit of your experience. I should probably find someone else to hassle now, to keep it all fair. I'm off to learn a bit more. I'm mindful that if I ignore too much expert advice I'll end up like this guy: https://makezine.com/2015/11/05/buil...-made-for-160/

[merlin777]

Search for fully supported round rails for examples of supported round rails.

Ger might have had profile rails on his mind such as those from THK or HiWin. These are often a much better choice for machine tool construction. I say often because sometimes it is simply more economical to use round rails where profile rails aren't needed. Also supported round rails can often provide for a tunnel to run the ball screw through.

There are many trade offs to be made with the various mechanical components that you can buikd a machine out of.

Is this what you had in mind, wizard? https://www.amazon.co.uk/gp/product/...A2GSQUBVY0H4PC

[ger21]

No, something like these:
https://www.ebay.com/itm/16mm-Fully-...oAAOSwl7JZnAG5

Stay away from anything that says it's for 3D printers. It won''t be anywhere near rigid enough for a machine with cutting forces.

[skrubol]

One issue with converting a rotary table to CNC is most of the cheap ones have terrible backlash.

[merlin777]

Hmmmn that's annoying. All the other 4th axis units I can see are waaaaay more expensive.

[wizard]

Is this what you had in mind, wizard? https://www.amazon.co.uk/gp/product/...A2GSQUBVY0H4PC

Not at all. Ger21 has a link to supported round rails which would be a minimal solution. Profile rails as like the solutions sold by THK, HiWin and others. Examples of which can be found here: LM Guide (Linear Motion Guide / Slide Guide) | [ THK || Global English ]

[wizard]

Much to consider there, thanks, Wizard.

I'm a planning-type person rather than a 'just wade in and do it' type person so I'm on a journey of education and discovery before I touch a piece of hardware. I learn something with every forum reply I get from you guys, so thanks for that.

We can help to an extent but ultimately you will need to dive into machine construction if you want to DIY a machine.
This can be a very daunting task for people who have never had exposure to machine tools.

I'm not in a position to do - or get done - machining and that might ultimately mean just saving up to get a decent 4 axis hobby level router but I'd like to check out other avenues first. It might just be that its worth a few quid to get hands-on of some components just so I can understand how everything works and where the problems are. The devil is usually in the detail.

I could be wrong here, but I'd be very surprised if you can find everything you need without having to machine something. It should be noted that you can buy all sorts of slide assemblies ready to go but you still need to mount them, build assemblies to clamp the spindles in place and etc. That being said much can be had off the shelf from suppliers like https://us.misumi-ec.com/, MSC, McMaster-Carr and the like.

The early design I have uses all readily-available components and draws on successful projects people have already documented.

A project is only successful if it meets the builders need. That builder might have dramatically different needs than you so don't assume glowing reports mean anything. For example the small 8mm rods you are looking at can be hell for vibration in machining applications that might be a huge problem for the quality goals you are trying to meet.

I liken this to the comparison between a CNC router for a boat builder and a violin makers. Technically both machines are for wood working but in the norm the violin maker will need a higher quality machine. The boat builder can right claim that he get excellent results while the violin maker would sneer at his machine. The challenge is to understand what is required to get the results you want.

For instance, you can source mounting plates to attach a nema 17 or 23 to the milling table .I've chosen. I'll definitely be looking for a stiffer support structure now. The tool height was an issue originally but I was going the put a manual vertical adjustment under the tool for those rare occasions I'll need anything different to exact centre height. I went through the helical spindle turning process from square stock to finished item and at the moment I can't see a need for an offset. I considered side mounting the tool on the cross slide to keep height down. I tired to design-in short and tight rather than long and loose as good practice.

My spindle was going to be a vertically mounted rotary table with compatible 4 jaw chuck and a stepper motor mounting kit. Solid but heavy. I'm still looking for alternatives because it seems a bit overkill.

Overkill is generally not a problem with machine tools. The primary issue is that the rotary table fit the machine and does not introduce interference with the spindle. That being said you probably should consider something other than a rotary table.

I share your view of the lathe conversion route.The amount of machining is a no-no for me for a start. It was my first approach and converting all 3 axes to CNC unless there's a kit would be too much of a hill to climb.

I really appreciate the benefit of your experience. I should probably find someone else to hassle now, to keep it all fair. I'm off to learn a bit more. I'm mindful that if I ignore too much expert advice I'll end up like this guy: https://makezine.com/2015/11/05/buil...-made-for-160/

Just to highlight other materials, there is nothing wrong with machines built from wood products if the goal is to machine wood products. For the type of results that you describe though you would likely need a better machine than the one linked to. Again the goal is to have something that meets YOUR expectations.