Modifying a Screw-in Lathe Backplate to fit on a small 3 bolt spindle - Mini Mill Drill Lathe

Finding the center of a plate without a center and mounting a backplate to the spindle of my HQ400 that it is not meant to fit. It does not go exactly as planned but it works.

BOSTAR AXA Size 250-111 Wedge Type Tool Post Tool Holders Set for Lathe 6-12"

The previous links are affiliate links, as an Amazon Associate I earn from qualifying purchases.

[frankross]

Use the 4 bolt holes to get a circle and measuring in from that would be a lot easier in my mind. You know the four holes are correct. Mount the plate in your 3 jaw from the outside and use your tool bit to scribe a circle around the 4 bolt holes, centers, outside or insides of them makes no difference. Set your dial on your cross feed and use that to come reduce the size to the size you need.

[CraigsWorkshop]

PS: If the tailstock used to be accurate, and isn't now, maybe your lathe bed (or the bench it's on) has settled in, since installation. Might be worth checking with a precision level, because the rear right leg may have lowered a tad, and that could have the effect of moving the tailstock away from you.

Also - if the height of the tailstock is off vertically, and can't be adjusted, please don't scrape anything off the bottom of the tailstock, instead - shim up the headstock. Much easier, and it's reversible in case it goes wrong.

[CraigsWorkshop]

Hey Eddie. This comment may well be too late, but using a centre finder would work.. The kind where you have a blade at 45 degrees to a fence, and the fence has a 90 degree internal angle (Do you know what I mean?). From there, you can draw lines that converge on centre. If the outer rim is true - which you showed with the indicator, then you can then measure in from the outside, instead of measuring out from the centre.

Alternatively, take a look at the method shown in my motor mount video, where I find the centre of a circle from three points. The method is probably a good starting point to solve the problem you have - hopefully it's food for thought at least.

Cheers,
Craig

[jimmyrogers]

You could have indicated the outside of the plate, centered the plate in the lathe then measured the diameter and calculated the center then move your cross feed in toward the center less the dimension of the pattern? It would have been best to screw the plate on the spindle and then calculate the center.

[peterjones]

You'll get a better finish and less 'pick up' on cutting tools if you use white spirits as cutting oil (paint thinners for oil based paint) I've also used diesel fuel as grinding and cutting oil for various aluminium alloys (castings, 6061, 70** series). It works well because of all the detergents in it

[wk]

Use the factory 4 bolt circle, which is accurate, and work in to your 3 bolt circle that you want. You cannot use that plug.

[johnstrange]

Sunday Video! Sunday vid... wait! Good video btw.