Modification of Quantum 210x400 lathe

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A few years ago I fulfilled a long-time dream and purchased a metalworking lathe. I bought a Quantum 210x400 lathe as it fitted my budget and was locally available. It is equipped with a fairly strong variable DC motor that allows for turning speeds from 150 rpm up to 3000 rpm.

  • DRO and glass scales
  • Milling table
  • Miscellaneous

Shumatech DRO550 and Sino glass scales

Like most of the far east lathes, the Quantum machines are fairly decent products in terms of materials and construction. However, one of the major shortcomings is positioning repeatability and accuracy due to backlash in the fine motion controls. This requires continuous measurements during operation, which is tedious and error prone. One way to improve on this aspect of the lathe is to install a DRO (Digital Read Out).

A DRO consist of a measuring device and a data display. Different classes of measuring devices are available and commonly used:

  • Digital calipers
  • Magnetic scales
  • Glass scales

From those options glass scales have the reputation for being the most accurate, which is why I selected them for my DRO system.
There are different brands available and I selected SINO glass scales that are manufactured in China and have a very good reputation.

Displays are available from many vendors, but I always liked the open source concept and therefore chose to build a Shumatech DRO550 readout panel. Scott Shumate designed this fantastic readout and the firmware is constantly updated with new features. Additionally, a very active Yahoo group provides support for the product.

Unfortunately there is no standard way to attach glass scales to this lathe and to make matters worse, space is very restricted on small machines, which limits mounting options. In order to find the best solution, I used Alibre 3D Cad software to create a 3D model of the relevant lathe parts and simulated the fitting of the scales. That helped a lot for identifying most problems like part collisions and allowed ultimately for a quick and straight forward execution of the task.

In the following section I will detail the conversion process with photos and text.

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  • Those images show my Quantum lathe before and after modification.
    I used a standard television wall mount bracket to support the display of the Shumatech DRO. You can also see the optional LCD that adds another two axis to the standard three axis display.

Compound table

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  • Due to space restrictions the mounting of the scale on the compound table was by far the most difficult task to be accomplished during the conversion process.
    In order to provide the reading head with its required space, the scale either had to be mounted horizontally or at a distance from the compound table carriage. I opted for the latter, as mounting the scale horizontally would have compromised its water/coolant tightness.
    I used a SINO KA-200 glass scale which is the smallest glass scale available.
    In order to be able to mount the scale, the original compound table had to be modified in the following manner:
    • First the original Allen set screws for the gibs had to be replaced by headless set screws. Once the gibs were adjusted, they were fixed in place with screw locking compound.
    • A suitable piece of rectangular aluminium profile was cut to size and fitted against the side of the compound table in order to serve as a separator for the scale. It has circular openings on the top in order to be able to reach the gib screws.
    • Next the circular base of the compound table was drilled for the reading head support and aluminum pieces were fitted to support the reading head.
    • Finally the glass scale support rail and the scale itself were attached.
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  • Because of the scale separator, the compound table angle can still be adjusted and the reading head has been positioned towards the right side therefore allowing easy adjustment of the circular scale.
    It is important to align the head and body diligently, so they run true along the entire scale displacement.
    One can see on those photographs how restricted the space is on this machine.
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  • As you can see, separating the scale from the compound table permits free rotation of the tool holder despite the fact that the glass scale is mounted slightly higher than the compound table base. This was necessary in order to leave enough room for the fine motion control of the crossfeed table.
    The red plastic brackets are transport safeties that are removed during operation.

Crossfeed table

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  • Again due to space restrictions, a SINO K200 glass scale was selected for the crossfeed table. Here as well, the gib screws were replaced by headless Allen screws, but no separator was necessary. As you can see on the photographs, small openings were cut into the scale mounting bracket in order to be able to adjust the gib if necessary.
    However, another problem surfaced, as the scale cable did not have enough room. In order to provide the cable with the space required, a small notch had to be filed into the carriage.
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  • Another mounting alternatives would have been to mount the scale on the lathe chuck facing side of the crossfeed table. However, I did not like the idea of exposing the scale to the risks associated with that option.
    Since the table locking screw was not accessible anymore after mounting the scale, I replaced it with a new locking screw on the chuck facing side of the table. Again I selected a headless Allan screw this time brass tipped to avoid damaging the dovetail of the table.
    As you can see, everything just fits with very little margin for errors. This is where simulation with Alibre helped a lot.

Bed carriage

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  • For the lathe-bed carriage I selected a SINO K300 scale since here were no space restrictions.
    Here it was important to compensate for the irregular surface of the lathe bed by supplementing the scale support bracket with shims were necessary.
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  • While on the other two axis the reading head is stationary and the scale body moves, in this case the scale body remains stationary and the head moves which requires as this connection between the reading head and the lathe carriage.
    This was accomplished with small aluminium pieces cut to size.
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  • Here close-ups of the mounting arrangement can be seen.
    Again, the requirement of perfect alignment between scale body and reading head has to be emphasized. It is especially important on a large scale like this one, as misalignment can easily damage the glass scale.

Simple milling table attachment

Unfortunately the Quantum 210x400 lathe does not allow for easy mounting of a rear tool post or milling support, as its crossfeed table does not have T-slots. I modified my machine in order to be able to mount work pieces firmly to the table, as it is required for milling operations.

The modification is very simple and basically provides a platform that can be adapted to any mounting scenario by drilling and tapping additional holes into the platform.

The following images shall illustrate the basic setup.

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  • After removing the compound table you are left with the crossfeed table with its circular support for adjusting the angle of the compound table.
    I cut a 1cm thick steel plate to size and drilled the required openings for fitting it on top of the original crossfeed table which had been drilled and tapped to accept M5 screws through the add on steel plate.
    Then several holes were drilled into it and tapped for M5, M6 and M8 screws to allow attaching work pieces and angle pieces.
    Evidently, this system requires you to remove the compound table prior to mounting the milling support. Recently I have shortened the steel plate and mount it with the compound table in place. This is fine for small work pieces. For bigger work pieces where one needs more slide travel, the compound table has to be taken off.
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  • Those photographs show an angle bracket mounted on the milling table. Work pieces can be fitted conveniently to it for machining.
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  • Another steel plate has been attached to the angle bracket for further work piece mounting options.
    As you can see, there are plenty of work holding possibilities and variations that can be tailored to the size and shape of the work pieces.

Miscellaneous modifications

Bed carriage arrest

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  • Originally the main carriage could only be locked in place with an Allan screw that can be difficult to reach depending on the position of the other carriages. The screw head also tends to fill with metal shavings, which makes it difficult to fit the key into it.
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  • A locking wrench has been made by brazing a small piece of an Allan key to a piece of steel. This custom Allan key was then fixed with a lock screw to the original Allan screw and provides an easy and quick way to lock the bed carriage in place.

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