Re: Drilling machines, cheap Ebay routers
- I quite agree. To that I would add flexing. From the single available photo
it looks as if the lead screw is attached by a thin piece of metal that
might have been cut from a coffe can. I have seen backlash more than 0.01"
caused by nothing more than flexing of metal quite a bit more sturdy looking
than that. The fact that the photo hides the motors and/or the method of
mounting them is a big red flag as well. I have seen some remarkably precise
machines made of MDF, but that looks like a piece of junk. It is not well
designed. If you want something like that you could build one just like it
from looking at the photo, end up with at least equal quality, and save a
lot of money.
----- Original Message -----
From: "epa_iii" <palciatore@...>
Sent: Friday, June 14, 2013 8:40 PM
Subject: [Homebrew_PCBs] Re: Drilling machines, cheap Ebay routers
>I do not have any particular experience of knowledge of this device except
>what I have seen here, but ...
> MDF should not be a problem unless you want to reduce the
> tolerance/accuracy level below 0.001 or so. Unless you have a widely
> varying humidity level in the area it is in. Wood does not automatically
> equate to "toy".
> As for the drawer slides, they come in a great variety of styles and some
> are a lot more accurate than others. They also can have different levels
> of slop in different directions. If they are properly selected and
> installed, they can be quite good, perhaps down to 0.002" or even better.
> Where the real problem really is is the drive screws and the steppers that
> drive them. If they used hardware store, threaded rod, then you
> automatically are reduced to +/-0.004" or worse accuracy. The accuracy of
> the steppers is on top of that so it adds to the error. Example: 20 TPI
> screw and 200 step stepper. That gives 20 X 200 divisions per inch or
> 4000. Each division if already at 0.00025" I strongly doubt that adding
> micro-stepping to that system would improve the accuracy to any measurable
> or noticeable degree.
> I could easily build a much better system with MDF and drawer slides by
> employing better screws and more attention to design and construction.
> However, I would use ground shafting for slides and close fitting bushings
> for the ways and better quality screws, perhaps Acme rod or ball screws
> from E-bay. I could easily get it down to 0.001" without any
> micro-stepping, which I do not trust except as a means of attaining
> smoother motion, not better resolution or accuracy. Micro stepping is not
> accurate because the torque is reduced at every level of increased steps.
> Yes, it is expensive for the level of accuracy it claims.
> --- In Homebrew_PCBs@yahoogroups.com, "Tony Smith" <ajsmith1968@...>
>> > That one looks a wooden toy, not a serious router. Very expensive for
>> > the
>> > quality it seems to have. Just my opinion.
>> That one has been around for a while, it's more an educational thing than
>> anything else. Made using MDF (chipboard?) and drawer slides.
> and made by Milford instruments. The "data sheet" is in fact theinstructions
> to build.I just noticed some of the dates on the manual are from late 2004, so yes,
> Milford instruments' own site is
this machine has been around for a while.