[Guldberg]

Thank you all for some great response!

You are right about the diagonel ribbing. The angles of each plate is totally screwed. I think i'll go for the straight ribs.

Each piece of steel is going to be lasercut. Why? Because a friend of mine operates a large laser on the nightshift, so i can get it for a fraction of the cost.
This also lead me to the thought of just bolting it all together instead of welding. As i see it, it is the mass that makes it stable, bolting should provide plenty of strength to that relativly small cutting force. An advantage is that i can make the laser cut the holes for bolting (atleast on the straight pieces), this way i only need to countersink them.

As for the headstock and spindle, the design is a rip off of the most common lathes of this size (Sieg series, quantum series etc.). I looked at some real cnc lathe spindle designs, they had from 4 to 7 various bearings. Ive haven't quite figured out the design yet, i have to think some more about it.

As for the surface grinding, im thinking about having only the surfaceplate ground and facemilling the base itself. This because the base is rather akward shaped, so i have to build a fixture myself, so i might as well facemill it myself then. Would this be a solution?

As for spindle, i will use a VFD. Someday when i become rich, maybe ill buy a used powerfull servo of ebay and use that. Live tooling could be fun:-)

I dont intend on using large boring bars. I have access to a full size lathe if i really need to make big parts. If a use a off the shelf spindle i get a bore of 20mm, if i make one myself i'll make the bore 25 to accomondate full ER40 collet diameter

[Khalid]

wow... u complete and i will follow...keep it up man

[Guldberg]

Maybe this will explain it.
Surface ground on both sides of the "baseplate"
Surface milled on both sides of the base itself

The base welded together (do i need to stress relieve it?) and the baseplate boltet to the base itself

[DSL PWR]

If you weld it you will need to stress relieve it. The ground plate bolted to the frame would be a waste of time imo. Since the frame will be much stronger than the plate once you bolt it on it will deform to the frame. I think if you face mill every thing, and do a good setup on a decent mill, you will have your surfaces pretty close (couple tenths).

If you decide to bolt the unit together you will need to machine each part (laser cutting won't be good enough), and put at least 2 locating pins on EACH joint. If you simply bolt the base together it WILL shift over time, then you will have a piece of scrap.

[widgitmaster]

I concur, your weldment must be stress relieved after face milling.
If you were to grind the top of the weldment where the top plate is fastened, then it will retain its flatness after assembly.

Another approach would be to weld the top plate, then you could mill 1/16" deep on all areas not covered by the linear rails and headstock, and after stress reliving, grind just the raised surfaces.

Just a thought!
Widgit

[Noodles87]

With the way you mounted the tailstock. How will you move the carriage? Unless the piece is pretty long. And are only turning so far to the end. You'll run into some trouble.

[Guldberg]

The reason i seperated the base and topplate from each other is that i have my doubt that the grinding company can handle the akward shaped bed. I thought that bolting a perfectly straight 20mm top plate to an almost straight facemilled surface wouldn't distort it, but maybe im wrong.

So two approaches

Option 1:

1: Weld the base together
2: Facemill both top and bottom, drill, tap etc.
3: Stressrelieve (can it be done after coating maybe?)
4: Facemill again, very light cut
5: Coat it. How hot before it distort? Powdercoating would be nice

6: Drill and tap top plate
5: Have topplate + the two railblock/risers precision ground
7: Bolt the railblocks/risers to the topplate
8: Bolt the topplate to the base

Option 2:

1: Weld everything together
2: Drill, tap etc.
3: Facemill all relevant surfaces
4: Stress relieve
5: Powder coat (maybe before stress relieve)
6: Very light facemill top and bottom

Option 2 would be alot easier. And maybe i should just be satisfied with the precision i could achive with this method:-)

[Guldberg]

As for the tailstock, either i leave it out or ill figure something out. Its not the main priority right now:-)

[widgitmaster]

Stress relieve first, because it's done in an oven!
As for the grinding, just make two or three wedges that mount on the bottom, so the top is parallel and horizontal! That's if the grinding company doesn't have a large sine plate or other fixtures!

The wedges will help you during the milling & drilling too!

Widgit

[Guldberg]

That is also what i intended to do in the first place. Make some solid wedges to bolt on.

Stress relieve first, coat afterwards. Check. Im thinking of powdercoating, but would that make it distort?

[LeeWay]

What temp do you stress relieve at? How long is it left in?
I always use 400 F. for 20 minutes for powdercoating small parts. It would probably take longer to get that much steel up to temp, so it would probably take 30 to 35 minutes to powder coat.

[handlewanker]

Yep I agree, bolting is not an option, too much doweling and precise squaring up of parts that are only bracings, but still have to be fitted.

I would go down the path of welding, but give a lot of consideration to how many internal bracings are rquired.

The first method would be to design for a light structure.
This is the most difficult, because using thinner materials means the crossbracings really must be strategically positioned so that they strengthen the structure as opposed to just spacing the sides apart.

A girder bridge is a typical example of this, light enough to carry the load without having to carry excess construction load, in other words not over engineered.

The second method would be to make the longest members of a fairly heavy thick material, hot rolled black bar material, not the cold rolled bright mild steel type that looks good for making things but plays havoc when the stresses are released when machined and welded, and use less ribbings but thicker ones, deeply veed out and arc welded.

Weight is not a problem here, so the heavier, over engineered construction will not move about due to flexing under load.

After the welding and any rough cutting out of cavities etc, the whole construction should be heated in a furnace and given a good soaking for a few hours.

This will allow the material to relax and only then can any machining be attempted.

If you follow the spindle construction of two angular contacts at the chuck end and two radial at he drive end, you won't go far wrong, and this is more or less the basic spindle layout now, give or take a few more bearings along the shaft as the designers dream them up.

You show a ground plate in post #23 bolted on, I'd have this made from a piece of hot rolled plate,welded on last before heating in a furnace, so that the assembley is totally closed, then machine the top surface for the linear rails.

This doesn't need to be surface ground, but I would mill the top and bottom surfaces true, and only grind the top if you really want a guaranteed flat surface for mounting the rails.
This type of construction is most satisfactory for a one off construction, and as good as a casting, without the making of patterns and the aging that is necessary.
Ian.

[handlewanker]

Hi, how about a two pack epoxy resin paint finish?
Goes on like painting a car body, no heat required, (I think).
Whatever finish you use make sure it will handle oil and coolants without rusting under the paint lifting the paint.
Ian.

[Guldberg]

Thanks again. Your long descriptions of the processes involved are greatly appreciated. I will defently go with welding the whole structure together, proberly from hot rolled steel as you describe. Im still not sure whether or not ill grind the parts or i should be satisfied with just the facemilling. I guess it depends on the price:-) Next time i get in the shop i think ill try to make the base out of mdf and see if its possible to weld it at all. Now if only my camera wasn't in for repair.

As for the paint/coating i'll leave that to the professionals, my dad in law runs a large coating company which specializes in PTFE coating

[handlewanker]

Hi, best of luck with your project, it'll keep you busy for a while.
Ian.

[Guldberg]

Thanks. But before i really can begin i have to finish my router AND sell my current cnc lathe to make up some money. But ive started to by all the part, mostly on ebay ofcause:-)

[Guldberg]

Hurray, sold the other lathe for 2000$. Ive been shopping big time

Stepdrivers:



Cambell breakout board:



Steppers, 4.6Nm/640oz-in:



Ballscrews:

z-axis, Ø20 pitch 5mm


x-axis, Ø20 pitch 5mm


Linear Rails, 20mm hiwin rails (203£/400$ :-s ):




4jaws indepentent chuck, 125mm:



ER32 collect chuck:



Baumer A50/80 precisions homing switches, repeatability 0,001mm:

[skip20]

Have you thought about casting the base then machine the surface you need.
Build your wood plug. Set in sand & then remove.
Pour in the metal & your off & running.
Could do the same for the head.
Great looking idea!
Skip20

[Guldberg]

Casting you say. Would be nice, only problem is that i dont have access to the equipment needed:-)

Im thinking of buying this spindle, anybody have an input on buying used lathe spindle?

http://cgi.ebay.com/ws/eBayISAPI.dll...:X:AAQ:US:1123

[handlewanker]

Hi Gulberg, you did say you were going to make the lathe yourself, which bit? LOL, only joking....with all that exotic gear it'll be a real corker.

Casting the bed in alluminium might not be a bad idea, (getting sombody else to cast it that is, don't even think of doing it yourself), alluminium is a pretty ductile and forgiving material, and does not have the stresses present that an all welded or cast in iron structure has.

I know I'm going to get shot in the rrrss for saying that, but apart from the expansion movement as the ambient temperature changes, (which only becomes a problem on a flimsy space frame structure), the main body of an alluminium casting can be made quite hefty, as there is no weight compared to iron or steel to worry about.

This would only be affected by a gradual change in ambient temperature as the seasons change, and if some temperature control were present, I.E. normal wotkshop environment of 22 deg C, then movement would be negligable

As a bonus the pattern can be quite easily knocked up in MDF which is so stable and grain free, and if it's made in a bread and butter fashion the shape can be quite complex without having to resort to intricate carving techniques.

Once the pattern is established it can be used as a preliminary assembly jig to get all the attachment points and seatings for the bearing blocks etc established prior to having the bed cast.

Even if the casting needs to be reworked, the material can be reused as the ally is absolutely recyclable for a rework.

I wouldn't dream of casting one myself, when you think of the melting capacity needed, and the mold requirements, much easier to have one cast commercially.

I wouldn't consider using the ally bed for any sliding or rotating parts as such, but as a base for attaching the rails and bearing blocks etc.

No matter how you design the bed, Murphy's law states that as soon as you've finalised the design and started building, another design element rears it's ugly head, and so it's back to the drawing board for a redesign, or maybe an agonising decision to live with the design shortcoming and compromise.

At least if it's cast in ally the only cost for a recast is the casting process, as the material would be supplied from the previous defunct casting.

True it will cost to get it good, but if you cast in iron or fabricate in steel it would be a total disaster if the design becomes too impractical to live with.
Ian.