Saturday, May 28, 2016

Part #5 - The Proposed Fixes


To improve the poor milling quality 3 areas need addressing, table flex, table ringing, and column flex. I looked at ways of improving these areas while keeping a functioning drill press.

The Table Brace
I need to reduce the flexing of the cast iron table with minimum permanent changes. Here is what I have come up with.


The rods are 3/4" solid thread-all. The rest is machined aluminum. The end of the rods attached to the bottom of the table via some blocks epoxied to the bottom of the table. That is the only permanent change with this mod (really semi-permanent since I'm sure a hammer would knock them off). The the rods terminate into the vertical brace which attaches to the pivot joint of the table which on mine is not adjustable but does provides a suitable mounting point. The lower end of the brace is fixed to the column via a collar which is a snug but sliding fit allowing the table to be raised and lowered. The rods are adjustable length and will be used to tram the table surface. The force on the rods is directed to the center axis of the column so there won't be any torque on the brace.

This setup should substantially reduce the flexing and ringing and provide a stable table surface. Also will allow the table to safely hold the weight of the XY table + rotary table + work piece + what ever else I want to pile on there.

Column Stiffening
After many hours of looking around I have determined my best bet is to fill the column with polymer concrete, also known as epoxy granite. This stuff is highly damped, adds mass and should add some stiffness. I have read conflicting theories on the stiffness improvement and it was I believe all conjecture, so since I took some stiffness measurements I'll be able to report in improvement quantitatively.
I'll be ordering a 5 gallon bucket Fillit (tm) from Castinite (www.castinite.com/precision.html). It has to be mixed, it's about 10% epoxy and 90% quartz aggregate from 1/2" and down. Then will be "poured" down the tube and then tamped to remove air pockets. My plan is to seal one end by welding or screwing a cover on the end and scoop in a small amounts, tamping and repeat until full. This should be fun. Details to follow.

And if I have some left over I might add a layer to the bottom of the table, not sure about that yet.

First Steps
The only tricky part is these parts will have to be machined on this drill press. To reduce the table flexing and vibration I will rig up some adjustable length poles under each of the 2 outer corners of the table to the base. This will reduce the table flexing and I'm hoping allow for reasonable some machining to be carried out.

But to do this machining I'm going to need an accurate quill stop and depth indication. So my first milling project is adding a quill stop/lock and a DRO for the depth.


This will be a permanent modification since the drill press really needs this. The stop rod is a piece of 1/2"-20 SS threaded rod and I have a couple of threaded stop nuts from a Bridgeport setup. The DRO is an e-bay special for about $20. This additional will help me control the depth of my cuts/holes.

3D CAD Drawings
By the way the 3D drawings were made in Fusion 360. I have almost no experience with real 3D CAD programs (Solidworks, SolidEdge, etc) and it took about 40 hours to go from zero to a parametric driven model of the drill press and with all my additions. The best part is Fusion 360 is free for enthusiast use (Fusion-360). Just in case you were wondering.
 

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