I don't know what to expect

[Grumpy Mike]

I am trying to build a CNC miller and I am OK with designing the electronics but I have limited machine tools and experience with the mechanical side. So I decided to get all the mechanical parts from MDL.

It proved to be a frustrating experience, they don't answer emails most of the time and don't do what you ask them. You arrange to send components back for them to re machine and then they don't collect it from the post office and it gets returned to you three months later.

To make matters worst the machine received a knock in transportation which I believe might have damaged things but I don't know what sort of quality to expect, that is, what is damage and what is just bad workmanship.

The X axis is very stiff so I stripped it down to the lead screw and I think it is bent. I have put a movie of me turning it by hand on the web. [ame="http://www.vimeo.com/8106162"]Screw thread on Vimeo[/ame]
You can see the end wobble. My question is:-
Is this what you expect from a lead screw like this or is it damaged. If you can get better ones who to get it from as I said MDL don't answer emails and that includes requests to buy stuff from them. I can't just get a raw lead screw as I don't have access to a lathe. It makes the x axis very stiff to turn.

The other axis are also stiff in different ways, the Z axis gets stiff at the same point every revolution and the Y axis gets stiffer towards the end. When I say stiff I mean I can only just turn it by hand by gripping on both sides of the lead screw. Trying to turn the shaft (6mm) is just a no go. Hits on reassembly of this to correct this would be appreciated as well.

Thanks

[irving2008]

Mike,

Welcome to the forum.

No way is that expected. It should be dead straight with no perceptable wobble. What diameter is the screw?

The first test is to disconnect the driving nut from the carriage and check that the carriage runs on the slides cleanly end to end. If it does then either the leadscrew is bent or its not parallel to the slides. Alignment of the latter is a case of loosening the bearing blocks and tapping into alignment while running the screw back and forth.

I'm guessing MDL is Marchant Dice Ltd?

[Grumpy Mike]

Thanks for that. Yes it is Marchant Dice Ltd.
The diameter of the screw is 12mm.
I am not sure if the assembly will allow the removal of the drive nut without the lead screw being in place, but I will try and assemble it without the lead screw and see if I have a problem with the carriage as well. I can only access it at weekends and then I don't have access to the internet so my progress might be slow.
Any idea of how to tackle / align the other two axis?
Thanks again.

[ptjw7uk]

You are not alone, most of us when we start do not know what to expect oe even what questions to ask.
I have had no problems with Marchant except that the ball screws I won on frightbay were unmachined and that meant more bits for my lathe, a collet chuck for one and then carbide cutters so as to machine them.
In hind sight I should have paid for them to machine them but its easy after the fact plus I have now got a collet chuck.
In fact I should have waited and bought a mill already converted but if we all waited until.... nothing would be learnt all.
I for one dont think any of us doing cnc conversions relaise the baptism of fire that awaited us!!!
You could look into trying to straighten the screws but you will need some more tools but leave the manchester spanner (hammer) alone!
Aftre all you have nothing to loose as its bent and wont work well.

Peter

[irving2008]

It is possible to straighten a bent leadscrew with a rubber mallett, a curved surface and some judicious and careful thumping and constant checking. Its a lot easier if the curvature is across the whole length, but Mike's looks like its at the end.

WHile I agree, Peter, there is little to lose, 12mm leadscrews being readily available, the issue is Mike has no machining capability (although there was a thread where someone successfully 'machined' a leadscrew end using some 12mmID bearing blocks, and electric drill and a file...). In an ideal world Mike would return these parts as 'not fit for purpose' and get relacement/refund as appropriate, but as he has said this is a problem...

Like you, Peter, I have bought stuff from MD without major problems, but I am increasingly hearing of people having more and more issues with them. It would seem that MD is overwhelmed by his success and is unable to provide an effective level of customer service.

[Robin Hewitt]

Once a screw is bent your chances of getting it truly straight are remote but you can probably improve matters to the point where it works. You need a good solid work bench, five blocks of wood with grooves across the grain, two G clamps and a straight edge.

First you find where the bending needs to happen and clamp a free end of the screw to the bench using two blocks so it bows upwards at the bend. These first two blocks stop it turning and stop the G clamps slipping off while protecting the thread.

Mark the top of the bend in felt tip so you can find it again if it should turn rather than bend.

Then it's two blocks underneath, either side of the bend, one in the middle on top and away you go.

The trick is to go slow, get a feel for how whippy it is. A little bending and a lot of checking with the straight edge.

Don't try to save time by skipping on the grooves, everything will roll about and stress you out something chronic.

You really should not have this problem, good luck

Robin

[Robin Hewitt]

It is possible to straighten a bent leadscrew with a rubber mallett, a curved surface and some judicious and careful thumping and constant checking.

I have heard American's talking about straightening gun barrels by whacking them on a pillow block, might work, not something I'd try :rofl:

[Grumpy Mike]

Hi guys thanks a lot for that. The screw is bent in possibly two directions at the end so I think trying to straighten it might not work, that coupled with my basic lack of mechanical aptitude. The lead screw has a shaft and baring on one end (the other end than on the video) but I don't know if that is a push fit or a screw fit. I assume I need to take it out in order to fit it to another one.

[Grumpy Mike]

After a lot of weighing up about whether to abandon this pile of scrap I have I have decided to give it another go. I have stripped it down and am going to get a new lead screw.

Does anyone know how to get the bearing and motor spindle off the end? Is it a screw fit into the end of the spindle or is it a push fit, or even machined down from the trapezoidal spindle?

[irving2008]

After a lot of weighing up about whether to abandon this pile of scrap I have I have decided to give it another go. I have stripped it down and am going to get a new lead screw.

Does anyone know how to get the bearing and motor spindle off the end? Is it a screw fit into the end of the spindle or is it a push fit, or even machined down from the trapezoidal spindle?

I'd imagine the motor is coupled through a coupling locked on with an allen screw. the bearing should be a push fit. MD offer machining of trap screw so I'd imagine its machined down to suit. Put up some pics, as I don't think we've seen one of theirs.