Tools - Knurling Tool Holder

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Modified Knurling Tool Holder for QCTP

[Jan. 29, 2014]

[Jan. 30, 2014 - added small section on knurling]

This is a simple project to address a problem I have been experiencing when knurling on my 7x10 mini-lathe: No matter how much I tighten down the tool post and the compound rest, the knurling tool always seems to "twist" sideways when knurling. I believe this happens because the knurling tool as purchased is designed to fasten into a standard tool holder to the left of the tool post; this arrangement necessarily results in a turning force being applied to the tool post and this, along with a bit of play in the knurling tool itself, results in the tool being rotated out of alignment.

Since I was already making tool holders for my QCTP, I decided to use one of the spares I made to create a customized holder for the knurling tool. The key feature of this holder and related adapter is that the knurling tool is held directly in front the tool post in order to eliminate any rotational force being applied to the tool post.

The photo to the left shows the completed tool holder and adapter in use. As a bonus, the knurling tool is a lot easier to set up, as the adapter simply drops into the QCTP.

Note that there is no depth stop on the tool holder - tool height is not critical for this application, and the knurling tool height is simply adjusted by eye.

Making the adapter

This adapter was made specifically for my QCTP and type of knurling tool (a model 3770 knurler from LittleMachineShop.com), so these instructions will need to be modified as necessary for any other type of setup. Further, the dimensions I chose were based in part on the raw materials I had on hand. However, I am providing the specific measurements I used as a guide to others who may wish to make a similar holder:

Plans in PDF format: https://drive.google.com/file/d/0Bykt5WZ092aWeHRrVVVKbkFlX1U/edit?usp=sharing
Plans in LibreOffice Draw format: https://drive.google.com/file/d/0Bykt5WZ092aWcUdVcGo1cUNHejg/edit?usp=sharing

Below are some additional photos of the adapter/holder.

Here is the model 3770 knurling tool as supplied by LittleMachineShop.com.

Knurler, Large Capacity with 6 sets of knurls

This photo shows the completed adapter/holder and knurling tool (on the right), and the factory supplied tool holder adapter on the left.

This photo shows, from left to right:

Dovetail tool holder for QCTP, modified for knurling tool adapter
Knurling tool adapter
Knurling tool
Factory supplied tool holder adapter

From left to right:

Knurling tool adapter
Dovetail tool holder for QCTP, modified for knurling tool adapter

Here is piece of brass knurled using the new tool setup. It's still a bit rougher than I would like, but it's not bad (keep in mind this is a magnified closeup shot). More to the poit for this article, I found that the "twisting" problem has been resolved.

Here's a better knurl, made after I had a bit more practice with the new holder; this one turned out pretty good if I do say so myself.

Here is the technique I used to make the knurl:

Adjust the scissors so that the knurling wheels are just touching the work piece when the wheels are positioned in line with the center of the work piece.
Back off the knurls and tighten the wheel one full turn
With the lathe running at lowest speed, advance the knurls onto the workpiece
Move the knurls along the workpiece using the automatic carriage feed

While the knurling proceeds, I use a pump spray to put generous amounts of WD-40 onto the knurls - both to lubricate the knurling and to wash out any chips. I put some folded paper towel on the carriage under the knurling tool to collect the WD-40 overflow.

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