Christmas in April

Over the last couple days, parts have been arriving. The biggest expectation was to see the acme threaded rod. I have to hand it to OnlineMetals.com and McMaster-Carr for their quick and accurate service!

Here are some photos of the aluminum angle from onlinemetals.Actually it came in 96" lengths. It will be cut per the cut list. The next items came from McMaster-Carr. The threaded rod comes in 36" or 72" lengths, so I based the table to utilize these sizes. As it turns out, I decided to use one full length and the other cut into two pieces, one for the Y-axis and the other for the Z-axis. (In case you don't know, The X-axis will be the long axis of the table, the width of the gantry will be the Y-axis, and the router up/down is the Z-axis-There, now you are a CNC expert)

I am happy with my selection of the 1/2" threaded rod because I was

concerned it would not be rigid enough, but it seems to be. Careful handling this threaded rod because there are little shards and it is quite sharp. I may sand it a touch or use some Scotchbrite pad on it to smooth it a bit. Technically it is 1/2"x10tpi 2-start. This means it has two thread tracks wrapped around it, so each track has 5 revolutions. My steppers are 1.8* (degree) per step, or 200 steps/rev., which means in single step mode, there are 1000 steps per inch, which will allow a resolution of 0.001", and 0.0005" in 1/2 step mode if it will handle it. The price for the drive nut at MMC was more than the appropriate anti-backlash drive nut from DumpsterCNC, so I just went with 3 of the DCNC antibacklash leadnuts ($18.50ea) and also decided to purchase 3 of the couplers ($17.50ea) to simplify the build. They are quite expensive, but probably worth it in terms of time saved, so with shipping it came to $114.00. This is not a cheap project. You will be looking at $900-$1000 to do it right. Luckily, I have purchased some parts over the course of time to lessen the blow.

 I also got a bunch of other stuff as you can see. The fastening technique Brian used is brilliant, and his jig for creating the joint holes is cool also. I will cover that later. I ordered 5/16-24 x 0.75" button head allen bolts to fit the bearings. As it turns out, the 0.3125"(5/16) bolts fit the 8mm bearing holes perfectly. I got some 5/16-24 plain nuts to use as spacers on the bearings as shown below.

I ordered a 10mmID bushing for use in the jig, a nice 10mm TiN coated drill bit and a high quality TiCN coated 3-flute 5/16-24 vanadium spiral point (pushes chips) tap to create the threaded holes in the angle. You use an 'I' letter drill bit to predrill the holes for tapping.

The dowel nuts are 16mm long with the hole at 6mm (from heel) and 10mm in diameter. The 50mm machine screws are 1/4-20 threaded. My plan is a 0.25"dia x 2" hole through the outer piece, with a 10mm x 0.625" deep hole partially through the side piece.

Initially, I have two schemes for mounting the motors. One is using basic allen head bolts with nylocs. The other is using special T-nuts. These are nice because there is little externally to create space, and there are no large teeth to crack up the wood.

I also received the couplers and antibacklash leadnuts from DumpsterCNC.

One super bonus, is I will be able to try out my new hand tapper-it should significantly reduce the effort, and increase the accuracy of the project. It was around $85 ($106 w/shipping). It allows nice close tolerance perpendicular tapped threads, with shaft counterbalancing, so only cutting force occurs.

 Today I ordered the support bearings for the threaded rods from VXB. They are close to the same size of the rail support bearings, but they have an ID of 0.375" and an OD of 0.875", which will be nice, so I can use a forstner bit to create the recess. I will lathe of a bit of the ends of the rods to fit perfectly in the above bearings. 

Today is friday, so I will be making some parts this weekend. Stay tuned for more exciting build info, same bat project, same bat channel.

05/02/2010 Quick Update:
I had to get the table saw squared away over the weekend and the weather here in Montana was not optimum, but I was able to cut one sheet of MDF down to the basic table size. Sunday evening, I was able to get the saw set up outside with the threat of big black clouds, but luckily the rain did not materialize until today (Monday). Follows are (3) photos. 1) table saw set up on plywood for leveling. You cannot believe how heavy the MDF is. It was all I could do to handle it alone. I decided to do a long cut first, leaving about 0.25" for burn so I could do a second cut when the sheet was smaller and more manageable. Doing by myself had the advantage of not having to coordinate a second set of hands, but left the full responsibility for accuracy with my underpowered guidance. I am happy with the outcome as you can see in photo 2). It looks like it came out pretty straight. It is very important that the X-axis edges come out parallel. After the sheet was smaller, I did a second cut to exactly 39". I wound up clamping a saw straightedge across the stock for the length cut and using a skilsaw. I am less than happy with the accuracy, but it is not that important for the end. One good thing is MDF is only $32/sheet, so even if parts come out substandard, it won't be too much effort to later recreate them with better accuracy, and they are easily replaceable.
Photo 3) Another view of the cut setup which should give you a feel for the overall size of the table. The next process on this piece is to trim the edges to 45* with either the table saw or the router. I have not decided yet. I will do some experiments on smaller pieces to decide.

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3-D design evaluation completed

The basic design has been completed and a bill of materials generated. The design will look like the following:

SolidWorks view of design in it's infancy

One of the coolest aspects of this project, is that once it is functional, I can use it to build upgraded parts for itself, so I am not to concerned if some of it is not super duper. The gantry will have a block material clearance of 9" of Z. It will have just under 72" of X, and a full 36"+ of Y. My initial router will be a Harbor Freight trim router I picked up for $20 (or maybe $30, can't recall). Here is a photo:

HFT 1/4" Trim router 0.4kw 26,000 rpm M#44914

The nice thing about this spindle is that the lower section is set up nicely for simple spindle clamps. I will probably not use any of the accessories.

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