Re: [CAD_CAM_EDM_DRO] Beginners screws ( was ACME ( was Re: leadscrew,

On Wed, 21 May 2003 09:37:03 -0400, you wrote:

>Harvey, thank you for pointing out weak spots of the design - first thing I
>do, will go to the
>Metal Supermarket and try to verify accuracy of the angles.

Metal supermarket was where I got the 4 inch angle that wasn't
right....

>I was playing
>with one
>not that far ago and it appeared to be quite good- hope its consistent.
>There are definitely much better designs then offered, but this one is
>within my manufacturing and budget limits - even easier then sliding
>bushings on 2 parallel shafts ( making
>shafts truly parallel may be a challenge without milling machine with DRO).

Actually, it isn't.

Here's what you can do.

consider the design as a shallow U. The rails are mounted on the top
pieces to complete a square.

take the two sides, bolt them together. Finish them as well as you
can, taking care to make the sides as parallel on the top and bottom
as possible, or at least, the bottom, assuming that's the reference
edge.

Space and drill the holes for the bars. Since both pieces are exactly
the same size, and bolted together, the holes will be pretty much dead
on.

To make the rails parallel, just make the end pieces parallel. Use a
cheat stick to get them the same distance apart, and align to an edge
you know is straight.

That ought to get it close.




I'll try ascii art...

_______________________________________________________
--------------------------------------------------------------------------------------------
(c) | |________|
/ \ \ / | |
/ \ \ / | | (a)
/ \ \ O / | |
/ \ / | |
(b) \ / / \ | |
\ / O \ | |
\ / / \ | |
\/ \ | |



The top plate is the nice horizontal line. (a) is an angle bracket
mounted on that, giving you a vertical line. The triangular line next
to it is a piece of 45 degree angle. (b) is the square tubing, set on
edge. All of it's angle are 45 degrees to the vertical. Notice that
if you butt the tubing against the angle bracket, the sides will
continue, they are parallel to each other.

On the face of the angle bracket attached to (a), the shaft of a
bearing is indicated by the "O". Mounted on that shaft is a bearing
assembly that runs like a wheel. that's the three \\\ lines. Those
bearings will ride square on the square tubing's walls.

This gives you the minimum number of bearings to resist up, down, and
(for this one) leftwards forces.. RIghtwards forces are handled by
the mirror image of this assembly on the other side of the table.

8 bearings ought to do it.

>I have some difficulties visualizing your idea of the 45 degree guides. Can
>you be so kind
>to draw a sketch of it - will be a great help.
>Regards, Alex

Hope that this helps a bit.

Harvey

>
>----- Original Message -----
>From: Harvey White <madyn@...>
>To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>Sent: Wednesday, May 21, 2003 10:11 AM
>Subject: Re: [CAD_CAM_EDM_DRO] Beginners screws ( was ACME ( was Re:
>leadscrew,
>
>
>> On Tue, 20 May 2003 16:45:52 -0400, you wrote:
>>
>> >OK,
>> >just uploaded the file of DIY linear guide.
>> >It is done for somebody with limited machining capabilities, but with
>> >burning desire to learn CNC, like myself.
>> >Alex
>>
>> Couple of comments, if you would.
>>
>> 1) that angle is not precision. None of the stuff is, unless it's
>> specifically made that way. I had some 4 inch aluminum angle that was
>> off a good 1/8 inch at the end of the 4 inches... So your bearings
>> might not ride squarely. Square tubing might, and I do say *might*
>> be more square. It's also more rigid, I suspect.
>>
>> 2) On the bottom (l/r) rail, the forces will twist the angle
>> counterclockwise, which might be something you want to look out for.
>>
>> 3) The inside of an angle is not a controlled dimension (and seeing
>> what I found out with the 4 inch stuff, sometimes the outside is not
>> controlled either....) It is neither necessarily smooth nor even
>> parallel to the side, and that's not considering the fillet at the
>> angle.
>>
>> There's a simpler method I've seen that was used for a sliding table
>> for wood saws. You do need to make an accurate 45 degree angle.
>>
>> You take two square tubes, put them on a 45 degree angle, and these
>> become your rails. You take an aluminum angle, and mount it on the
>> bottom of the table, inside the rails. On this angle, you take
>> another piece of aluminum angle (or steel, if you want) and mount it
>> so that the edges are 45 degrees to the vertical. The angle is
>> rotated to match the sides of the rails, and there's perhaps an eighth
>> of an inch gap between the angle and the rails on each side.
>>
>> >From those edges, you put the bearings in, so that they will ride on
>> the surfaces (one top, 45 degree angle, but flat against the rail,
>> ditto bottom).
>>
>> The adjustments might be easier to do, and it seems mechanically
>> simpler.
>>
>> I've tried the same kind of idea on a circular rod, but the bearings
>> do not ride well, too much pressure on one contact point.
>>
>> Harvey
>>
>>
>>
>> >
>> >
>> >----- Original Message -----
>> >From: CL <datac@...>
>> >To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>> >Sent: Monday, May 19, 2003 10:47 PM
>> >Subject: Re: [CAD_CAM_EDM_DRO] Beginners screws ( was ACME ( was Re:
>> >leadscrew,
>> >
>> >
>> >>
>> >>
>> >> alex wrote:
>> >>
>> >> >Thank you, Ross - I'm more or less sure now what to do.
>> >> >Will place sprocket directly on the shaft of stepper, then pull
>carriage
>> >in
>> >> >a loop by the chain.
>> >> >
>> >> You might want to slide that sprocket in a little further so you can at
>> >> least get a smidget of support on the end of that motor shaft with an
>> >> outbound bearing....
>> >>
>> >> It still is not enough, but that would be better than nothing.
>> >> Most steppers are not made to take much of any side load on their
>> >bearings.
>> >>
>> >> Ultimately, you need to put the sprocket between two bearings on a
>shaft
>> >> that is driven direct by the stepper with a Helical coupler.
>> >> Or, mount the motor to a short section of square aluminum tubing with a
>> >> bearing on each side. One bearing can be right on the motor shaft, the
>> >> other on an extension with the Sprocket.
>> >>
>> >> That obviously takes more work.
>> >>
>> >> Then again, if motors are cheap enough, just replace the motor when it
>> >> goes "south".
>> >>
>> >> Chris L
>> >>
>>
>>
>>
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>OFF Topic POSTS: General Machining
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>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
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