[kram]

Hi,
Im looking for a manual bench top machine but I consider it may be better to have one made for me rather than buying a chinese machine. I am following many of the threads on here, including build threads.

Criticism, and quotes (for design/machining) is welcome and wanted. I am located west sussex, england.
My budget (total) is around £1000, about the same as a sieg X3.. but doesnt include any tooling.
total size should be around 1000x500x500 or so..

Steel/cast iron etc.. costs about ~£1 per Kg raw
Im also looking at using granite as the base, a 24"x18"x4" surface plate costs £100/80Kg.
I cant find any bigger granite surface plates than 24"x24"?. Also I think surface plate flatness may be OTT.
Ive found many much cheaper sources of granite, so the question is can it be machined flat easily using a flycutter..?

If made from steel plate, what grades of steel is suitable?
With cast iron, I would need each surface to be machined flat and square, stress relived etc.., which is what I hope to avoid with granite or partly with steel.


I have only quickly looked into rails/dovetails. I would like it to be an off the shelf type rather than machined dovetails, but also cheaper than linear rails.
Could I use lengths of prehardened toolsteel/silversteel rod for rails?

I dont know how much machining/drilling each part will cost, but heres some numbers:

£200 - 150kg base/table etc..
£100 - rails/dovetails.
£100 - Spindle (each, will add the second later)

My budget is ~£1000 for the working machine, so that leaves about £600 to get it made.

thanks
Mark

[kawazuki]

And a column or gantry? And bodies? to mount the tables/axis on, And leadscrews / ballscrews, And a motor for the spindle, And controller for the motor? ? ? ?
Personally I'd say your budget is about £1-2K light for a finished and accurate machine

[kram]

I found this, http://www.itpgroup.co.uk/products/s...s/granite.html
Interesting, Ill ask how much the additional machining costs


thanks Kawazuki
I do not have any previous machining experience so your criticism is very welcome. Please tell me if the following is realistic:

I plan the spindle to be horizontal and fixed height like a lathe, and using a vertical slide as a Y axis for milling. This would be part of the build, and part of the budget.
However I will need some kind of spindle housing - so your right.

How will this compare, in terms of rigidity, to a normal mill with a vertical Z axis?.
I believe this is a much better method for a combo machine than the chinese type with a weak x2 milling colum.

I looked into leadscrews, I belive a set costs about £150 or less, its something I need to find more about.
I will also look into used leadscrews, for example from a new machine cnc conversion, if there is any suitable length.
I dont intend to go full CNC on this, so ball screws would be expensive and probably dont have enough friction for a manual machine. However I would like powerfeed, and for this I would likely use resonable stepper motors, a large 1kA tordial for power, and a cheap controller for jogging - additional to budget.

I also want to look into accurate measuring. It may be better for me to use digital scales for feedback, and the cheapest unaccurate screws instead.

My above spindle budget of £100 - for one spindle (will add second higher speed spindle on this in future) may be optimistic, although I am 100% sure I can get a suitable motor with control for under £20, the question is about the spindle housing, bearings, and belt/gear drive, especially if the lathe spindle will power a leadscrew for threads.

Im not including the lathe tooling in the budget, I know chucks etc.. cost a lot.

I already have a suitable table to put the machine on, I think, it should hold 200kg..


Problem of finding the right compromises, and I may have to scale down the machine to fit budget, it may increase in the future.
I would like the base, table etc.. being made of granite, to be of suitable standard for small production work, which the chinese machines below 2k are certainly not out of the box.

Mark

[rowbare]

You left out the most important thing: what kind of materials do you want to cut? What you are describing *might* be able to cut aluminum in an emergency but that is about it for metals and I wouldn't recommend it.

Very few, if any, people build manual machines. There are actually more constraints when building manual than cnc. eg... when building a cnc machine you can use pretty much any pitch lead screw you can get your hands on. The electronics will deal with it. For a manual machine you need to find a pitch that makes sense given the scales you are going to use on the hand cranks. Or you can use DROs but a decent DRO setup costs as much as a set of steppers and a controller.

All in all your design seems a bit unbalanced, you have this massive base but you are totally cheaping out on the rails. Anything you gain by having this granite base you lose in spades by not being able to guide your tool accurately. Also your budget for a spindle may or may not be adequate. At that price you can buy a Proxxon
rotary tool and not much else. While it is good for a start, it is still basically a hand-held rotary tool...

You are thinking this through, and that is a good thing. I would suggest that you share with us what kinds of a materials you want to work with and that you check out the Project log forums to see what people have been building and how successful the various designs have been.

http://www.cnczone.com/forums/forumdisplay.php?f=221

http://www.cnczone.com/forums/forumdisplay.php?f=172

http://www.cnczone.com/forums/forumdisplay.php?f=48

This site is a great resource with a lot of helpful people. Don't be afraid to ask questions.

bob

[kawazuki]

I plan the spindle to be horizontal and fixed height like a lathe, and using a vertical slide as a Y axis for milling. This would be part of the build, and part of the budget.
However I will need some kind of spindle housing - so your right.

I'm certainly no long, time served master machinist either, just a relative newcomer that has a useful hobby. I look at the many varied machines available - hobby or full production and they generally have a common thread - vertical spindle operation! Very few are horizontal! I would guess the majority workload on most machines is X + Y moves reserving the 'less rigid' Z moves to a minor role. I don't see how your Y axis positioning fixture is going to be 'more' rigid or easier to secure work to, as the workpiece will be hanging in space at 90 deg to the clamps with gravity acting on it producing unequal forces on the rails and table. For a DIY project - I wouldn't try to re-invent the wheel - i'd follow the crowd at least until i'd built something and then discovered how it could be improved rather than the reverse and finding the end result worse than a 'chinkie' mass market product!

[knudsen]

I hate to see new members commit suicide. Can you find one of these in the UK?

http://www.grizzly.com/products/Dril...th-Stand/G0704

Drop the table and you have a fine benchtop mill in your price range. Please spare me the heartache

[kram]

Im interested in the g0704/BF20 types. I still think they are expensive, and have problems - mostly column deflection and poor ways?
but they seem like the best option for new..


However Ive found quite an old machine, its not free but less £££ than its scrap iron value :O It will need work, but it has got useful parts, including a spindle (no motor), so I might buy it anyway.

the interesting thing is its small knee table. The whole machine is too big,but the knee table looks like it could be seperated easly, and bolted onto a suitable column.

The cast iron base is attached to the X way, not the Z - so I think they are separate pieces.


The leadscrews look like inch, so will be replaced

I plan to have a look at this at the weekend, also looking at a bf20 clone.