Member postings for old mart

Most countries seem to be giving fairly accurate figures, even Russia recently re evaluated their figures upwards. Only the Chinese figures seem to be politically modified. There was a Chinese comment on the news saying that the Covid 19 did not start in Wuhan.

If you can hold a 20mm bar securely, it would be better than a 16mm one. Maybe a special toolpost could be made for large bars. I have made three special toolposts and also a mounting to directly use a larger toolpost on the cross slide expressly for using 25mm boring bars, but which will hold all the standard tooling.

You could check for backlash in the machine leadscrews, not making allowances for it can lead to unexpected errors.

I only recommend split dies used in at least 2 stages. Having the diestock resting against the front of a drill chuck in the tailstock and advancing the tailstock quill gently helps to keep the die straight. Some steel types do not like being threaded however good the dies are. With a tailstock die holder, you could try not locking the tailstock, just push it gently as you turn the chuck.

Edited By old mart on 13/01/2021 16:12:26

Wikipedia has info on Schrader valves. I have seen them used in compressed air regulators at 3000psi, and the cores look just like the short version and are the same size.

A solid carbide boring bar would certainly do the job, but that depth is at the limit of one of my 12mm ones and a 16mm one would probably cost more than a set of larger carburettors. If a 16mm steel bar is used, the compound and cross slide gibs should be tightened up a little and the minimum of tool overhang to reach the required depth is important.

What carbs are they? Flange or spigot fitting? The old flange type had a habit of being overtightened and the face not being flat, which has to be addressed when mounting them. Keep the speed fairly low and check for any runout before cutting metal. The problem of tiny drillings into the bore getting clogged up and the problem of removing tiny burrs from the holes without changing their fuel or air flow is a worry.

 As already mentioned, the long stickout of a 16mm bar can cause problems, another reason for taking tiny cuts. I, too would prefer 20mm bar size, but it could be difficult to hold in your lathe.

Edited By old mart on 12/01/2021 21:28:51

Jason B recommends a 16mm boring bar, and I think that is the best size. The actual tip height of boring bars is somewhere near half the nominal tool height, so if the toolpost has enough depth to hold the bar, it can fit a lathe that could not manage a 16mm standard tool.

ARC sell a nice bar 16mm which takes CCMT09 type inserts. 060-325-39516

An insert suitable for zinc or aluminium CCGT09T308. 060-326-01938

The ARC site shows the dimensions of the tool. It will be long enough for your carb bore. I would recommend very small cuts and lubrication such as wd40 or ac90.

Back in the sixties, I had a pair of Amal monoblocks bored out to 1 3/16" for a Royal Enfield Constellation. The centre part of the carbs was in place and bored simultaneously. Some time later, one of the central parts failed, the cause was blowholes in the zinc casting.

Hardwood lapping sticks are available up to 25 x 6mm section which may not be big enough. They are laminated and very hard and strong.

www.moleroda.com

Those pesky cosmic rays causing trouble again!

It's always interesting to see another way of doing something which adds versatility to existing tooling.

Why not make the first new key 0.010" longer and hand file it back if it turns out too tight. A thin coat of felt tip on the side would show up any tight parts. There is unlikely to be any specification. Check for wear on the stem of the key and the corresponding hole in the lock

Edited By old mart on 10/01/2021 21:18:22

I also post on an American forum, and are careful to use international language, such as "sodium hydroxide" when the locals refer to "lye". And some references to "mil" actually mean 0.001"( one thousandth of an inch).

Edited By old mart on 10/01/2021 21:01:41

Lathejack, you have had good results with close fitting radial registers, but you do not mention any experiance of using loose radial registers. So you are an expert on the subject?

Common spindle preload setup with taper roller bearings is just enough to end up warm to the touch but not hot, after 15-20 minutes at top speed unloaded. This would probably hold good with angular contact bearings as well.

The rear shoulder is vital for alignment, but as long as the thread is vee shaped, it will bring the backplate into the same position radially each time. The wear of the threads will eventually cause variations, but that would be after thousands of fittings considering the very coarse type of thread used. I do check the alignment every time a chuck is dismantled for cleaning and have never had to re skim the front of the backplate. I have made several backplates and like to allow 0.001" clearance as tighter fits are hard to assemble and remove. The looser ones up to 0.020" have been bought of inherited, but repeat just as well.

Edited By old mart on 08/01/2021 18:05:50

Paint stripper might work, but the modern formulations are not as good as the older types. Only a test area can tell.

You ought to find out what type of blasting would be used, bicycle frame tubing is very thin wall.

Edited By old mart on 08/01/2021 15:15:51

I would remove the chuck and check for runout on the fromt face and for radial runout in any register shoulder. Remove the backplate and refit several times and check whether there is any measurable change. The mating parts will have to be clean and well lubricated to be sure any foreign bodies do not influence things. If the backplate repeats well, then fit the chuck and use it, then take it off and recheck the backplate. You may be lucky and save a lot of rework or replacement.

A long shot, but is there any way of increasing the engagement? That might allow you to reduce the diameter of the worm by 1/8".