Tuesday, September 18, 2012

Lathe progress - Bed and bedways

The other day I headed back into the workshop to do some work on my lathe, which has been languishing for a while as a result of my working too much, and having uni work to do. Anyway, I bought some bolts from ebay (M8x1.25x80mm), and they turned up not long ago. So I set out laying the holes out on the ways and drilling them, ready for tapping.

I ran into a couple of...snags...during this process. Firstly, and worstly, I snapped not one, but two 3mm drill bits off in the bedways. After much swearing and a lot of dremel work, I managed to remove them. The second issue came as a result of misreading a drill-size chart. I read 7.2mm for M8 taps, when in fact the drill size is 6.8mm... No real drama, I just have shallower threads than I wanted. It seems to work fine though.

My camera was nowhere to be found during this process, but it was all quite straightforward, errors aside. I had 25 bolts, and a metre of bed to join to a metre of bedway. Casting one bolt aside as a spare, I set about spacing the 24 bolts evenly over the length of the bed, about 30mm apart, and centred along the length of the  ways. If you're doing this at  home, make absolutely sure that the bolts are spaced close enough together to go through the bed with no troubles. Had I spaced them 50mm apart, they would have been going through the walls of the bed...bad idea.

Anyway, pilot holes drilled, I clamped the ways to the bed and got them aligned, then proceeded to drill holes through the bed, using four of the pre-drilled holes as guides. I tapped the four holes I had used as guides, and bolted the bed and ways together with four bolts. Next, I drilled the remainder of the holes using a complex multi-step method of my own invention...

I drilled a small dimple into the bed, using the holes in the ways as a guide. Then I removed the ways from the bed and put the bed onto my drill press, which I used to drill 10mm holes through the top surface of the bed. If you have a nice big drill press, drill straight through in one go. Unfortunately for me, I had to drill my holes in two steps. I did all the top holes, then had to fiddle around a LOT to drill through the bottom, while maintaining alignment. I ended up doing this by chucking and unchucking the drill bit for every new hole, which worked fine, but was as tedious as all-get-out.

That done, I tapped the rest of the holes in the bedway and gave it a test fit. Brilliant!

The next step is to put a 10mm dowel through each pair of holes and fill the bed with concrete. This will add mass to the bed, which is always a good thing, but it will also help reduce flexing. Another good thing! The dowels will be greased so that I can just push them out (hopefully!). If not, I can drill them out easily.

Now, in case anyone was curious about why I drilled 10mm holes for M8 bolts, good question. Basically, it gives me about 2mm of wiggle room along the length and width of the bed for getting alignment right, and it absorbs any error I may have made in aligning the holes correctly to start with.

Anyway, onwards and upwards.

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