Shop Info

Dovetail Lapping or Scraping

The mills and lathes that come from overseas most times don't have the best fitting gibs.
A lot of them, especially Sieg products, suffer from dovetails that are sloppily machined
which leads to binding at one end of travel or both with table slop in the middle. The G0704
has better tapered gibs versus the flat gibs on most other machines.They can still suffer from
some of the same problems, ususally because of a warped gib strip. All these troubles can be lessened or eliminated by lapping, scraping or both. Which to do, which to do. You'll find many arguments for/against both such as in this long thread on Cnczone. It's my thought that if the amount of material to be removed is small, then lapping should be good enough.
Basically, Lapping invloves loosening the gibs, pulling the table for example off, applying a gritting paste to the dovetails, reassembling, and pushing the table back and forth by hand many times
until you feel the binding areas no more, apply more grit paste and adjust the gibs a little tighter, and repeat. Generally starting with a coarse grit (240 or 320 if severe) and then with a couple finer grits, 600 and 1200 for example. that's what I used on my X2 years ago. Follow up with a thorough cleaning and reassembly. Scraping can be more involved and requires more skill, basically you apply a layout fluid such as Dykem to the mating part, assemble them and push them back and forth against each other. This will show you the high spots that you can then scrape down with a flat tool. Repeat the process until you have a uniform transfer of dykem over the entire length.

You'll find some links below for more details, some are for lathes but the process is very similar.

Lapping

Lapping with Wet/Dry Sandpaper - from mini-lathe.com

Lapping the Dovetails - Mike Taglieri's Procedure

Scraping

Basic Hand Scraping books and videos - machinerepair.com

Video - Scraping in a dovetail - detailed

Video - Scraping in a lathe's top slide with tapered gib

Lapping Compounds

American Lap Company

Newman Tools Timesaver

MscDirect Clover Lapping Compound

Scraping Tools

MscDirect - Machinists Scrapers

G0704 CNC Conversion Tooling

Below you will find the minimal list of tooling needed to machine the
G0704 Phase 1 and Phase 2 CNC Conversions.

Drill Bits
#29, #21, #7, F, 13/32, 7/8*, 1 1/16*

Taps
8-32, 10-32, 1/4-20, 5/16-18, 15/16-16*, 1.125-18*

Endmills
1/4, 3/8

Countersink
5/8 90 degree **

Centerdrill
5/16 double ended **

The majority of the items are drill bits and taps. You should pick up a complete set of each anyway for your shop, they are basic, must haves. Don't buy the cheap imports, spend a few more dollars for decent US high speed steel or cobalt bits, with a Drill Doctor, they should last for years. Drill bits size 1 - 60, Drill bits size A -Z, Drill bits size 1/16 - 1/2,
Tap and Die Set.**

* If you can cut internal threads on a lathe, you won't need these drills and taps.
** optional tools not absolutely necessary.

CNC Conversion Costs

The following are some ballpark CNC conversion costs for converting the G0704.
You'll find many links to the particular items on the Electronics Page and under "Accessories" on the Main page. This is what you'll need to spend to make a mill that can machine parts. Tooling and software will add to the costs as your needs increase, but this basic package will allow you to make chips. You'll be years adding to your tooling accessories. Software can cost more than the mill easily but there are plenty of free or very affordable programs to get you going.
Note: The mechanical side of the DIY CNC conversion with ballscrews can be done for less than $450 which is less than HALF the cost ($975) of comparable ready made kits out there. Sometimes it pays to Do-It-Yourself.

G0704 Mill - $1200 shipped
CNC parts (stock, hardware,bearings, couplers or pulleys, plans) - $200
Ballscrews and nuts for Phase 2 (machined) - $438 shipped *
or
C7 Ebay Ballscrews and nuts for Phase 2 (machined) - $225 shipped
Electronics (Motors, Drivers, Power Supply, BOB etc.) - $400 - 700 **
Computer - $200
Mach 3 (to run the mill) - $175 ***
Enclosure, wiring, E-stop etc. - $200
Tooling Package - $300
Measuring Package - $60.

Total for Phase 1 conversion and cheaper electronics - $2673
Total for Phase 2 conversion and cheaper electronics - $2960 - $3173 ****
Total for Phase 2 conversion and higher end electronics - $3260 - $3473 ****

* This is for machined ballscrews from CJA, you can save $200 by machining them yourself.

** The cheaper electronics are the package using the KL-6050 drivers and are what I've run on mine, it gives awesome performance with 300 IPM rapid speeds. The more expensive package uses the digital drivers.

*** Mach 3 can run 500 lines of code in the free version so you don't have to spend the $175 right away. Most everything will work and you can make parts with the free version.

**** The price difference is from the choice of machined Ballscrews and Nuts.

Note: Costs for the tooling needed to make the conversion parts aren't included as many of them are basic items like drill bits in most homes, others are in the tooling package.
The large taps may or may not be required especially if you use the C7 Ebay Ballscrews and Nuts which won't require threading of the ballnut mounts.